Skip to content

Linux Tricks

Backup

rsync

  1. With rsync how can I always replace the DEST file by the SRC file?

    • Use -a flag of rsync.
    • It is a quick way of saying you want recursion and want to preserve almost everything.
    • If you want to always replace all the files with the same path on path/to/dest/ by the files on path/to/src/, run the command:
    rsync -a path/to/src/ path/to/dest/

  2. With rsync how can I always replace the DEST file by the SRC file only if the SRC file is newer than the DEST file?

    • Use -au flags of rsync.
    • Skip files that are newer on the receiver (-u flag).
    • If you want to replace all the files with the same path on path/to/dest/ by the files on path/to/src/ that are newer, run the command:
    rsync -au path/to/src/ path/to/dest/

  3. With rsync how can I keep the newer file between DEST and SRC file on the receiver and keep a copy on the receiver of the older of DEST file and SRC file?

    • Use -aub flags of rsync.
    • -u flag: skip files that are newer on the receiver.
    • -b flag: with this option, preexisting destination files are renamed as each file is transferred or deleted.
    • If you want to keep the newer files between path/to/dest/ and path/to/src/ on the receiver (path/to/dest/) and keep a copy on the receiver (path/to/dest/) of the older files (by appending them a ~), run the command:
    rsync -aub path/to/src/ path/to/dest/

  4. With rsync how can I synchronize DEST directory and SRC directory?

    • Use -au flags of rsync.
    • -a flag: it is a quick way of saying you want recursion and want to preserve almost everything.
    • -u flag: skip files that are newer on the receiver.
    • If you want to synchronize path/to/src/ and path/to/dest/, that is (DEST and SRC become the same copy, keeping all files that were on DEST but not on SRC and vice-versa, and keeping the newer files (with the same path) of the DEST and SRC directory), run the commands:
    rsync -au path/to/src/ path/to/dest/
rsync -au path/to/dest/ path/to/src/

  5. With rsync how can I synchronize DEST directory and SRC directory, keep a copy of the older files and generate a log file?

    • Use -aub and --backup-dir flags of rsync.
    • It is a quick way of saying you want recursion and want to preserve almost everything (-a flag).
    • -u flag: skip files that are newer on the receiver.
    • -b flag: with this option, preexisting destination files are renamed as each file is transferred or deleted.
    • --backup-dir: in combination with the --backup option, this tells rsync to store all backups in the specified directory on the receiving side.
    • If you want to synchronize path/to/src/ and path/to/dest/, and keep a copy of the older files in a specified directory backup (on both directorise path/to/src/ and path/to/dest/) and a log file backup.log (available on both directorise path/to/src/ and path/to/dest/) that keep track of the synchronization process , run the commands:
    rsync -aub --backup-dir="backup" path/to/dest/ path/to/src/ \
  | tee -a path/to/src/backup.log
rsync -aub --backup-dir="backup" path/to/src/ path/to/dest/ \
  | tee -a path/to/src/backup.log
rsync -aub --backup-dir="backup" path/to/dest/ path/to/src/ \
  | tee -a path/to/src/backup.log
rsync path/to/src/backup.log path/to/dest/backup.log
    • Note 1: In the file backup.log, you can see what happen during the synchronization. This way you can see the files that have been deleted on the SRC directory but still present on the DEST directory that you copied back into to the SRC directory.
    • Note 2: The directory backup contains all older files.
    • Note 3: If on the SRC and DEST you had the file path-to/some-file that differed, after the synchronization you can see the difference (how the newer was changed from the older), by running the command:
    git diff path/to/src/backup/path-to/some-file path/to/src/path-to/some-file
    • Note 4: After the synchronization, if you are happy, you can delete on both side (SRC and DEST directories), the file backup.log and the directory backup. To do so, run the commands:
    rm -rf path/to/src/backup path/to/src/backup.log
rm -rf path/to/dest/backup path/to/dest/backup.log

  6. With rsync how can I delete files on DEST that are not present on SRC?

    • Use -a, --delete flags of rsync.
    • (-a flag): it is a quick way of saying you want recursion and want to preserve almost everything.
    • --delete flag: this tells rsync to delete extraneous files from the receiving side (ones that aren’t on the sending side), but only for the directories that are being synchronized. You must have asked rsync to send the whole directory (e.g. "dir" or "dir/") without using a wildcard for the directory’s contents (e.g. "dir/*") since the wildcard is expanded by the shell and rsync thus gets a request to transfer individual files, not the files’ parent directory.
    • If you want to delete files on path/to/dest/ that are not present on path/to/src/, run the command:
    rsync -a --delete path/to/src/ path/to/dest/

  7. With rsync how can I delete files on DEST that I've note exclude the first time with rsync ?

    • Use -a, --delete-excluded, --exclude flags of rsync.
    • -a flag: it is a quick way of saying you want recursion and want to preserve almost everything.
    • --delete-excluded flag: in addition to deleting the files on the receiving side that are not on the sending side, this tells rsync to also delete any files on the receiving side that are excluded with --exclude.
    • --exclude flag: exclude files matching a pattern.
    • If you first have send the directories node_modules accidentally from the path/to/src/ directory to the path/to/dest/ directory, you can delete them later. To do so, run the command:
    rsync -a --exclude="*node_modules*" --delete-excluded \
  path/to/src/ path/to/dest/

  8. With rsync how can I do a incremental backup?

    • Use -avz, --exclude and --exclude-exclude flags of rsync command.
    • -a flag: it is a quick way of saying you want recursion and want to preserve almost everything.
    • -v flag: increases the amount of information you are given during the transfer.
    • -z flag: compresses the file data as it is sent to the destination machine.
    • --exclude flag: exclude files matching a pattern.
    • --delete-excluded flag: in addition to deleting the files on the receiving side that are not on the sending side, this tells rsync to also delete any files on the receiving side that are excluded with --exclude.
    • If you want DEST directory to be the exact copy of SRC directory, but you just want to send the file that have changed SRC, delete on DEST the file you have deleted on SRC, and do not send (exclude) on DEST the node_modules directory on SRC, run the command:
    rsync -avz --exclude="*node_modules*" --delete-exclude \
  path/to/src/ path/to/dest/

Backup and archive

  1. What is a Backup?

    • A backup is a copy of data that can be used to restore the original in the event that your data is lost or damaged. If a company experiences data loss due to hardware failure, human error or natural disaster, a backup can be used to quickly restore that data.

  2. What is an Archive?

    • An archive is a collection of historical records that are kept for long-term retention and used for future reference. Typically, archives contain data that is not actively used.

  3. What is the difference between backup and archive?

    • Basically, a backup is a copy of a set of data, while an archive holds original data that has been removed from its original location.

Back up /etc directory

  1. How can I review or revert changes that were made to /etc?

    • Use etckeeper tool.
    • etckeeper: store /etc in git.
    • See etckeeper README.
    • If you want to install and initialize etckeeper on ubuntu, run the commands:
    sudo apt install etckeeper
    • If you want to commit changes made in /etc installing new package using apt, do nothing, etckeeper do it for you.
    • If you want to commit changes made in /etc, run the commands:
    cd /etc
sudo git add .  # or only a few files
sudo git commit -m "your message"
    • If you want to configure and tweak etckeeper, see files and directories /etc/etckeeper/ and /etc/etckeeper/etckeeper.conf.
    • If you want to skip some files or directories from being stored into git repository, add them to /etc/.gitignore.
    • If I want to revert changes to a previous state (commit), you must checkout to the previous commit and re-initialize etckeeper, to do so run the commands:
    sudo git checkout <previous-commit>
sudo etckeeper init

  2. How can I back up the /etc directory to usb drive?

    • Use rsync command.
    • rsync: a fast, versatile, remote (and local) file-copying tool.
    • Be aware that /etc directory contains secret informations. For instance, SHA-512 password are stored in the file /etc/shadow.

Large files with git

  1. What is git-annex?

  2. What is git-lfs?

  3. What is the difference between git-lfs and git-annex?

    • See discussions git smudge clean interface suboptiomal and large files with git (article).
    • git-lfs differs from git-annex in that:
    • With git-lfs, all the large files in the repository are usually present in the working tree; it doesn't have a way to drop content that is not wanted locally while keeping other content locally available, as git-annex does.
    • And so git-lfs does not need to be able to get content like git-annex can do either.
    • git-lfs also differs in that it uses a central server, which is trusted to retain content, so it doesn't try to avoid losing the local copy, which could be the only copy, as git-annex does.

Devices

USB drive

  1. How can I securely clear (wipe out) all the data on my USB drive?

    • Use dd command.
    • dd: convert and copy a file.
    • See format usb drives by linuxize.
    • If you want to wipe out all the data on your USB drive, plug it, be sure that is not mounted, and assuming that your target drive is /dev/sdb, run the command:
    sudo dd if=/dev/zero of=/dev/sdb bs=4096 status=progress
    • Last time, for a 32GB usb drive, the process took about 30 minutes to complete.
    • Once the disk is erased, the dd command will print ~No space left on device.

  2. How can I format a usb drive with EXT4?

    • Use parted and mkfs.ext4 commands.
    • parted: a partition manipulation program.
    • mkfs.ext4: create an ext4 filesystem.
    • See format usb drives by linuxize.
    • If you want to format an usb drive with only one ext4 partition that take the whole space, plug you're usb drive, be sure that is not mounted, create a GPT partition table, create a ext4 partition that takes the whole space and finaly format the partition to ext4. To do so, assuming that your target drive is /dev/sdb, run the commands:
    sudo parted /dev/sdb --script -- mklabel gpt
sudo parted /dev/sdb --script -- mkpart primary ext4 0% 100%
sudo mkfs.ext4 -F /dev/sdb1
    • When the usb drive is formated as above, when the usb is mounted it is own by root, belong to root group and as the permission file is drwxr-xr-x.
    • If you want to print the partition table and verify that everything is set up correctly, run the command:
    sudo parted /dev/sdb --script print

  3. How can I name a USB drive with an ext4 filesystem?

    • Use e2label command.
    • e2label: change the label on an ext2/ext3/ext4 filesystem.
    • See rename usb drive from help.ubuntu.com.
    • If you want to name (or rename) my-name your USB drive, assuming the target drive is /dev/sdb1 and is unmounted, run the command:
    sudo e2label /dev/sdb1 my-name
    • I you want to check the name of your USB drive, assuming the target is /dev/sdb1, run the command:
    sudo e2label /dev/sdb1
    • The name of an usb drive doesn't identify the usb drive. For this purpose see UUID of the usb drive or the PARTUUID.

  4. How can I know the UUID of an USB drive?

    • Use blkid command.
    • blkid: locate/print block device attributes.
    • See persistent block device naming from archlinux wiki.
    • If you want to print the UUID of the block device wich partition is /dev/sdb1, run the command:
    blkid -s UUID -o value /dev/sdb1
    • Filesystem partitions have UUIDs but physical devices do not.

  5. How can I set up the USB drive in such way that user with the same UID accross linux system can access to the USB drive?

    • Use mkfs.ext4 and chown commands.
    • mkfs.ext4: create an ext4 filesystem.
    • chown: change file owner and group.
    • See ext4 formatted usb drive on stackexchange.
    • If you want to format your usb drive to ext4 file system and give it the ownership of the same username (same UID) you share accross linux system, assuming that /dev/sdb1 is the partition and my-name is your username, run the commands:
    sudo mkfs.ext4 /dev/sdb1
sudo mount /dev/sdb1 /mnt
sudo chown my-name: /mnt
sudo umount /mnt
    • Take care, the above operations will kill your all the data on the usb drive.

  6. How can I preserve mode/ownership/timestamps when using cp or rsync with sudo?

    • cp: copy files and directories.
    • rsync: a fast, versatile, remote (and local) file-copying tool.
    • If you want to copy the directory my-dir to your USB drive mounted at /mnt and preserving mode/ownership/timestamps, run the command:
    sudo cp -r --preserve my-dir /mnt  # with cp
sudo rsync -rog my-dir /mnt  # with rsync

  7. How can I mount a usb drive without sudo privilege?

    • Use pmount command.
    • pmount: mount arbitrary hotpluggable devices as normal user.
    • If you want to mount your USB drive on /media/usbdrive assuming the target drive is /dev/sdb1, run the command:
    pmount /dev/sdb1 usbdrive
    • If you want to unmount your USB drive mounted with pmount assuming the target drive is /dev/sdb1, run the command:
    pumount /dev/sdb1

  8. How can I mount a usb drive?

    • Use mount command.
    • mount: mount a filesystem.
    • If you want to mount your USB drive on /mnt assuming the target drive is /dev/sdb1, run the command:
    sudo /dev/sdb1 /mnt
    • If you want to unmount your USB drive, assuming the target drive is /dev/sdb1, run the command:
    sudo umount /dev/sdb1

  9. How can I list block USB devices?

    • Use lsblk command.
    • lsblk: list block devices.
    • If you want to the block USB devices on your machine, run the command:
    lsblk

  10. How can I list USB devices?

    • Use lsusb command.
    • lsusb: list USB devices.
    • If you want to the USB devices on your machine, run the command:
    lsusb

  11. How can I know what is the available space on a USB drive?

    • Use df command.
    • df: report file system disk space usage.
    • If you want to know the available space that remains on a USB drive, assuming the target drive is /dev/sdb1 and is mounted, run the command:
    df -h /dev/sdb1

  12. Why the file system of my usb drive suddenly becomes read-only?

    • See usb drive write protected or read only on stackexchange.
    • This is probably because the drive has probably experienced a fault condition. That is your usb drive is not safe. So you must backup your data and change your usb drive.

Iphone

  1. How can I mount my Iphone on my linux machine?

    • Use idevicepair and ifuse command.
    • idevicepair: manage host pairings with devices and usbmuxd.
    • ifuse: mount directories of an iOS device locally using fuse.
    • See mount your iphone as an external drive from maketecheasier.
    • If you want to mount your Iphone on the directory /media/iphone in order browse its directories contents, you have to plug your Iphone to your machine, pair it, create the directory /media/iphone (if doesn't exist yet) and mount the Iphone. To do so, run the commands:
    idevicepair pair
mkdir /media/iphone
sudo ifuse /media/iphone
    • If you want to list the medias on your mobile (in my case there were on the directory /media/iphone/DCIM/106APPLE), run the command:
    ls ~/media/iphone/DCIM/106APPLE
    • If you want to unmount your Iphone, run the command:
    sudo umount media/iphone
    • If you want to install idevicepair and ifuse, run the command:
    sudo apt install libimobiledevice6 libimobiledevice-utils ifuse

Files

Get info

  1. How can I recursively list a directory in a tree-like format?

    • Use tree command.
    • tree: list contents of directories in a tree-like format.
    • In the root directory of an React app, limiting the max display depth of the directory tree to one by running the command tree -L 1 ., I get this output:
    .
├── jsconfig.json
├── node_modules
├── package.json
├── package-lock.json
├── public
├── README.md
└── src

3 directories, 4 files
    • In the root directory of an React app, limiting the max display depth of the directory tree to one and ignoring file in the node_modules directory, by running the command tree -I node_modules -L 2 ., I get this output:
    .
├── jsconfig.json
├── package.json
├── package-lock.json
├── public
│   ├── discreet-theme.css
│   ├── icon-tricks192.png
│   ├── icon-tricks512.png
│   ├── index.html
│   ├── manifest.json
│   └── robots.txt
├── README.md
└── src
    ├── App.js
    ├── App.scss
    ├── App.test.js
    ├── astUtils.js
    ├── astUtils.test.js
    ├── index.js
    ├── _myBulma.scss
    ├── orgContent.js
    ├── serviceWorker.js
    └── setupTests.js

2 directories, 20 files

  2. How can I check the space usage of a directory?

    • Use du command.
    • du: estimate file space usage.
    • If you want to check the space usage of your $HOME directory in a human readable way, run the command:
    du -sh $HOME

  3. How can I check the file type of a file?

    • Use file command.
    • file: determine file type.
    • If you want to check the file type of the files elisp.el and video.mp4, that respectively contain emacs-lisp code and mp4 video, run the command:
    file elisp.el video.mp4
    • After running the previous command, I got this output:
    elisp.el:  Lisp/Scheme program, ASCII text
video.mp4: ISO Media, MP4 Base Media v1 [IS0 14496-12:2003]

  4. How can I get a detailed information about audio/video files?

    • Use mediainfo command.
    • mediainfo: command line utility to display information about audio/video files.
    • After running the command mediainfo video.mp4, I got the output:
    General
Complete name                 : video.mp4
Format                        : MPEG-4
Format profile                : Base Media
Codec ID                      : isom (isom/iso2/mp41)
File size                     : 186 KiB
Duration                      : 11 s 603 ms
Overall bit rate mode         : Constant
Overall bit rate              : 131 kb/s
Writing application           : Lavf57.83.100

Audio
ID                            : 1
Format                        : AAC
Format/Info                   : Advanced Audio Codec
Format profile                : LC
Codec ID                      : mp4a-40-2
Duration                      : 11 s 603 ms
Duration_LastFrame            : -3 ms
Bit rate mode                 : Constant
Bit rate                      : 129 kb/s
Channel(s)                    : 2 channels
Channel positions             : Front: L R
Sampling rate                 : 48.0 kHz
Frame rate                    : 46.875 FPS (1024 SPF)
Compression mode              : Lossy
Stream size                   : 183 KiB (98%)
Default                       : Yes
Alternate group               : 1
    • After running the command mediainfo audio.mp3, I got the output:
    General
Complete name                 : audio.mp3
Format                        : MPEG Audio
File size                     : 2.31 MiB
Duration                      : 2 min 45 s
Overall bit rate mode         : Variable
Overall bit rate              : 117 kb/s
Writing library               : Lavf57.83.100

Audio
Format                        : MPEG Audio
Format version                : Version 1
Format profile                : Layer 3
Format settings               : Joint stereo
Duration                      : 2 min 45 s
Bit rate mode                 : Variable
Bit rate                      : 117 kb/s
Channel(s)                    : 2 channels
Sampling rate                 : 48.0 kHz
Frame rate                    : 41.667 FPS (1152 SPF)
Compression mode              : Lossy
Stream size                   : 2.31 MiB (100%)

  5. What option can I use to format the file time printed with -l option of ls command?

    • Use --time-style option of ls command:
    • --time-style: with -l, ls show time using style full-iso, long-iso, iso, locale, or +FORMAT where FORMAT is interpreted like in date.
    • If you want to list the file of a directory with the time format set to iso, run the command:
    ls -l --time-style=iso
    • After running the previous command on one of my directory, I got this output:
    -rw-r--r-- 1 tony tony 22293 11-11 19:10  clojure.org
-rw-r--r-- 1 tony tony 44155 11-13 06:11  emacs.org
-rw-r--r-- 1 tony tony 15442 08-03 12:10  frontend.org
-rw-r--r-- 1 tony tony  6053 11-10 10:01  git.org

View files

  1. What cat, head and tail commands are for?

    • cat: concatenate files and print on the standard output.
    • head: output the first part of files.
    • tail: output the last part of files.

  2. What less command is for?

    • less: a filter for paging through text one screenful at a time.

  1. How can make a symbolic link?

    • Use ln command.
    • ln: make links between files.
    • If you want to make a link to the file /home/tony/videos/video.mp4 (TARGET) with the name video.mp4 (LINK_NAME) living in the directory linked-video, run the commands:
    cd linked-video
ln -s /absolute-path-to/video.mp4 video.mp4
    • If the linked-video was empty before making the link above and if you run the command ls -l in the directory linked-video you should obtain something like this:
    lrwxrwxrwx  1 tony tony 37 Jul 24 08:24 video.mp4 -> /home/tony/videos/video.mp4

  2. How can I get the path (target) of a symbolic link?

    • Use readlink command.
    • readlink: print resolved symbolic links or canonical file names.
    • If you want to get the path (target) of the current python, run the command:
    readlink $(which python)

  3. How can I manage symbolic links of whole directory tree?

    • Use stow command.
    • stow: software package installation manager.

    • If you want to link all your dotfiles files in your $HOME directory to a versioned directory dotfiles, assuming dotfiles directory is a subdirectory of ~/some-directory, run the commands:

      cd ~/some-directory
stow -t $HOME dotfiles

    • If you want to unlink the stow links made in the previous section, run the commands:

      cd ~/some-directory
stow -D -t $HOME dotfiles

Compression

  1. How can I (archive) store multiple files in a single file?

    • Use tar command.
    • tar: an archive utility.
    • If you want to store all files frome the directory /etc into the archive file etc.tar verbosely listing the files being archived, run the command:
    tar -cfv etc.tar /etc

  2. How can I extract all files from a tar archive?

    • Use tar command.
    • tar: an archive utility.
    • If you want extract all files from the archive archive.tar, run the command:
    tar -xf archive.tar

  3. What is the difference between zip and gzip?

    • See difference between zip and gzip from differencebetween.net.
    • gzip can achieve better compression compared to zip.
    • zip is capable of archiving and compressing multiple files, while gzip is only capable of compression.
    • You can easily extract individual files from a large zip file, but not from a gzip tarball.

  1. What is fzf?

    • fzf is a general-purpose command-line fuzzy finder.
    • See fzf repository and this video on fzf.

  2. How to update linux locate cache?

    • Use updatedb command.
    • updatedb: Update a database for mlocate.
    • See stackexchange.
    • If you want to update the database use by locate command, run the command:
    sudo updatedb

  3. What locate command is for?

    • locate: find files by name.

  4. What grep command is for?

    • grep: Search for pattern in files.
    • If you want to search the sequence hello world in the files menu.h and main.c ignoring the case, run the command:
    grep -i 'hello world' menu.h main.c

  5. How to ignore binary files when searching with grep?

    • Use -I option of grep command.
    • -I: Process a binary file as if it did not contain matching data.
    • See stackoverflow.
    • If you want to search the sequence hello world in the files in your current directory ignoring the binary files, run the command:
    grep -I 'hello world' *

  6. How to find files that match string or regexp?

    • Use find command.
    • find: search for files in a directory hierarchy.
    • See example of command find by Alvin Alexander.
    • If you want to find files recursively from your $HOME directory where the name match the global patern virtualenv*, run the command:
    find ~/ -name "virtualenv*"

  7. What is recoll?

    • recoll is a desktop full-text search tool.
    • See recoll homepage, recoll usermanual and counsel-recoll if you want use it with emacs.
    • To install recoll, run the command:
    sudo apt install recoll
    • ~/.recoll/ is the default config directory.
    • ~/.recoll/recoll.conf is the recoll main configuration file.
    • ~/.recoll/xapiandb/ is the default directory for the index data.
    • To use it, you first have to index the xiapan database with recollindex.
    • To index the xiapan database of recoll according to the the config file ~/.recoll/recoll.conf, run the command:
    recollindex

Replace string

  1. How to replace string in multiple files?

    • Use commands sed, perl and find.
    • sed: stream editor for filtering and transforming text.
    • perl: the Perl 5 language interpreter.
    • find: search for files in a directory hierarchy.
    • See replace string on stackoverflow.
    • If you want to replace all occurrences of one string with another in all files in the current directory (Non recursive, files in this directory only.), run the command:
    sed -i -- 's/foo/bar/g' *
    • If you want to replace all occurrences of one string with another in all files in the current directory (Recursive, regular files (including hidden ones) in this and all subdirectories), run the command:
    find . -type f -exec sed -i 's/foo/bar/g' {} +
    • If you want to replace only if the file name matches another string (Non-recursive, files in this directory only), run the command:
    sed -i -- 's/foo/bar/g' *baz*    # all files whose name contains baz
    • If you want to replace only if the file name matches another string / has a specific extension / is of a certain type etc (Non-recursive, files in this directory only), run the command:
    find . -type f -name "*baz*" -exec sed -i 's/foo/bar/g' {} +
# all files whose name contains baz

fd command

  1. With fd, how to find all files except hidden files and directories?

    • It's the default behaviour of fd command.
    • fd: find entries in the filesystem.
    • See fd repository.
    • If you want to find all files except hidden files and directories, run the command:
    fd
    • Note that if you are in git directory, the search ignores the files ignored by .gitignore file.

  2. With fd, how to include all hidden files in the search?

    • Use the option --hidden of fd command.
    • fd: find entries in the filesystem.
    • See fd repository.
    • If you want to include all hidden files in your fd search, run the command:
    fd --hidden

    • Note that if you are in a git directory, this shows all files in the directory .git/ but skip the files ignored by .gitignore file.

    • If you want to include all hidden files in your fd search but exclude files in the .git/ directory, run the command:

    fd --hidden --exclude '.git/*'

  3. With fd, how to find every file entries?

    • Use --hidden and --no-ignore option of fd command.
    • fd: find entries in the filesystem.
    • See fd repository.
    • If you want to include every file entries in your fd search, run the command:
    fd --hidden --no-ignore

  4. With fd, how to restrict the search to the directories?

    • Use --type option of fd command.
    • fd: find entries in the filesystem.
    • See fd repository.
    • If you want to restrict your fd search to the directories, run the command:
    fd --type d

  5. With fd, how to restrict the search to the file only?

    • Use --type option of fd command.
    • fd: find entries in the filesystem.
    • See fd repository.
    • If you want to restrict your fd search to the files only, run the command:
    fd --type f

Directories

  1. How can I list the directories first when using ls?

    • Use --group-directories-first flag of ls command.
    • ls: list directory contents.
    • If you want to list the directories first when using ls, run the command:
    ls --group-directories-first

  2. How can I create a directory with its parents?

    • Use mkdir command.
    • mkdir: make directories.
    • If you want to create this nested directories dir-1/dir-2/dir-3 from the directory you are in, run the command:
    mkdir -p dir-1/dir-2/dir-3

  3. How can I go back to the last directory I was in?

    • Use cd command.
    • cd: change the shell working directory.
    • I you want to go back to the last directory you were in, run the command:
    cd -

Watch files

  1. How can I automatically run test when some files change on disk?

    • Use watchman-make command that come with watchman.
    • watchman-make : waits for changes to files and then invokes a build tool (by default, make) or provided script to process those changes.
    • See watchman documentation and watchman install documentation.
    • If you want to run pytest on a python project each time the subdirectories ./src and ./tests/ change on your disk, in the root of your project, run the command:
    watchman-make -p 'src/**' 'tests/**' -r 'pytest'
    • To install watchman-make which is part of the package watchman, use the package manager homebrew and run the command:
    brew install watchman

  2. How can I whatch a file and trigger a command when it was opened?

    • Use inotifywait command.
    • inotifywait: wait for changes to files using inotify.
    • If you want to print hello world in the stdout after the file path/to/watched-file was opened, run the command:
    inotifywait -qq -e open path/to/watched-file && echo "hello world"

Redirection

  1. What does 2>&1 mean in a command line?

    • Redirect the standard error stderr (the file descriptor 2) to the standard output stdout (the file descriptor 1). You can consider >& as a redirect merger operator.
    • See stackoverflow.
    • So if you have a command line my-command that send error to stderr and you want to catch the errors on stdout, run this command:
    my-command 2>&1

Images

Use images

  1. How to set the wallpaper?

    • Use the command feh.
    • feh: Image viewer and cataloguer.
    • See feh on archlinux wiki.
    • If you want path/to/images.jpg to be you be your image background, run the command:
    feh --bg-fill path/to/images.jpg
    • If you want to remove your background image set with feh, run the command:
    xsetroot -solid black

Manipulate images

  1. How to convert images?

    • Use the command convert.
    • convert: convert between image formats as well as resize an image.
    • See convert image on howtogeek.
    • If you want to convert the image image.png to the format jpg, run the command:
    convert image.png image.jpg
    • If you want to install convert, as it comes with the imagemagick package, run the command:
    sudo apt install imagemagick

  2. How to resize an image?

    • Use the command convert.
    • convert: convert between image formats as well as resize an image.
    • See convert image on howtogeek.
    • If you want to resize an image to 200 pixels in width and 100 pixels in heigh, run the command:
    convert image.png -resize 200x100 image.png
    • If you want to install convert, as it comes with the imagemagick package, run the command:
    sudo apt install imagemagick

Miscellaneous

  1. Where can I find linux ressources?

terminal

  1. How can I check which terminal I'm using?

    • Use cat and grep commands.
    • cat: concatenate files and print on the standard output.
    • grep: print lines matching a pattern.
    • See which terminal i am using on askubuntu.
    • If you want to check which terminal you are using, run the command:
    cat /etc/alternatives/x-terminal-emulator | grep exec

desktop

  1. How can I send a desktop notification?

    • Use notify-send command.
    • notify-send: a program to send desktop notifications.
    • If you want to send the message hello world to the desktop and that the popup window notification keep alive 3 seconds, run the command:
    notify-send -t 3000 "hello world"

environment variables

  1. How can I print all environment variables?

    • Use printenv command.
    • printenv: print all or part of environment.
    • If you want to print all environment variables, run the command:
    printenv

  2. How can I list colors used in my terminal?

    • Use dircolors command.
    • dircolors: color setup for ls.
    • If you want to print the color used by ls command in your terminal, run the command:
    dircolors --print-database

Ubuntu

  1. How to check your ubuntu version?

    • Use lsb_release command.
    • lsb_release: Print distribution-specific information.
    • See linuxize.
    • If you want to know your Ubuntu distribution version, run the command:
    lsb_release -d

Network

DNS

  1. How to get information of an url ?

    • Use the command dig.
    • dig: a DNS lookup utility.
    • See A record from dnsimple.com.
    • If you want to get the A record of youtube.com, run the command:
    dig A youtube.com

Host

  1. How can I know my IP address?

    • Use ifconfig command.
    • ifconfig: configure a network interface.
    • If you want to know your (local) IP address (use over the LAN), run the command:
    ifconfig -a | grep -E 'inet '  # this is the local IP address
    • If you want to know your (public) IP address (use over internet), follow the link ifconfig.co or run the command:
    curl ifconfig.co/ip

SSH

  1. How can I enable SSH server on ubuntu?

    • Use openssh-server package.
    • openssh-server: Secure shell (SSH) server, for secure access from remote machines.
    • See enable ssh on ubuntu by linuxize.
    • If you want to enable SSH server on the standard port 22, you have to start ssh service with systemctl command and allow incomming SSH connection by opening (allowing) the port 22 with the command ufw and enabling the connection with the command ufw. To do so, run the commands:
    sudo systemctl start ssh
sudo ufw allow ssh  # or sudo ufw allow 22/tcp
sudo ufw enable
    • If you want to install openssh-server and start the service ssh, run the command:
    sudo apt install openssh-server

  2. How can I connect to my server via SSH?

    • Use ssh command.
    • ssh: OpenSSH SSH client (remote login program).
    • See enable ssh on ubuntu by linuxize.
    • If you want to connect to your Ubuntu machine over LAN with bob as username and 192.168.1.100 IP, run the command:
    ssh bob@192.168.1.100
    • If you want to connect to your Ubuntu machine over Internet with bob as username and 2a01:c50e:e911:9600:fc4d:b07d:d36f:6358 IP, run the command:
    ssh bob@2a01:c50e:e911:9600:fc4d:b07d:d36f:6358

  3. How can I know that my shell is connected via a SSH connection?

    • Use printenv command.
    • printenv: print all or part of environment.
    • If you want to know if you're connected via SSH, check if the environment variables SSH_CONNECTION, SSH_CLIENT and SSH_TTY are defined. To do so, run the command:
    printenv | grep SSH

  4. How can I exit a SSH connection?

    • Use exit command.
    • exit: cause normal process termination.
    • If you want to exit a SSH connection, you can either type C-d or run the command:
    exit

  5. How can I mount remote directories over ssh?

    • Use sshfs command.
    • sshfs: filesystem client based on ssh.
    • See sshfs by linuxize.
    • If you want to mount the home directory of a user named tony on a remote host with IP address of 192.168.1.100, create a directory ~/remote-tony that will serve as a mount point and use sshfs command. To do so, run the commands:
    mkdir ~/remote-tony
sshfs tony@192.168.1.100:/home/tony ~/remote-tony
    • If you want to detach the mounted file system ~/remote-tony, run the command:
    sudo umount ~/remote-tony

  6. How can I setup a passwordless SSH login?

    • Use ssh-keygen, ssh-add and ssh-copy-id command.
    • ssh-keygen: Authentication key generation, management and conversion.
    • ssh-add: Adds private key identities to the authentication agent.
    • ssh-copy-id: Use locally available keys to authorise logins on a remote machine.
    • See examples setup passwordless ssh login and create different public key.
    • If you want to connect to the user jim on the server 192.168.1.100 without prompting a password, you have to generate a ssh key, send the public part to jim@192.168.1.100 server, append the public key on the remote file ~/.ssh/authorized_keys and add the private key to the authentication agent. After that, you can directly connect to the server. To do so, run the command:
    ssh-keygen -t rsa -f ~/.ssh/id_rsa_jim
ssh-copy-id -i ~/.ssh/id_rsa_jim.pub jim@192.168.1.100
ssh-add ~/.ssh/id_rsa_jim
    • If you want to list all identities currently represented by the agent, run the command:
    ssh-add -l
    • If you want to delete the identity ~/.ssh/id_rsa_jim from the agent, run the command:
    ssh-add -d ~/.ssh/id_rsa_jim

  7. How can I solve the problem that give the error: "Error connecting to agent: No such file or directory"?

    • Use eval command.
    • eval: execute arguments as a shell command.
    • See open a connection to your authentication agent on stackexchange.
    • If you want to open a connection to your authentication agent that is already running, run the command:
    eval "$(ssh-agent)"

  8. How can I start my authentication agent ssh-agent?

    • Use ssh-agent, eval and ssh-add commands.
    • ssh-agent: hold private keys used for public key authentication.
    • eval: execute arguments as a shell command.
    • ssh-add: adds private key identities to the authentication agent.
    • If you want to start your authentication agent, open a connection to the agent and add the key id_rsa_some_key to the agent. To do so, run the commands:
    ssh-agent
eval "$(ssh-agent)"
ssh-add ~/.ssh/id_rsa_some_key
    • If you want to list the identities represented by the authentication agent, run the command:
    ssh-add -l
    • If you want to Kill the current agent (given by the SSH_AGENT_PID environment variable), run the command:
    ssh-agent -k

  9. How to get ssh private key automatically added to the authentication agent?

    • Use the keywords AddKeysToAgent and IdentityFile in the ~/.ssh/config user's configuration file.
    • AddKeysToAgent: specifies whether keys should be automatically added to a running ssh-agent(1).
    • IdentityFile: specifies a file from which the user's RSA authentication identity is read.
    • See man documentation ssh_config.
    • If you want to get ssh private keys ~/.ssh/id_rsa_key_1 and ~/.ssh/id_rsa_key_2 automatically added to the authentication agent, you have to add these following lines to the file ~/.ssh/config:
    Host *
    AddKeysToAgent yes
    IdentityFile ~/.ssh/id_rsa_key_1
    IdentityFile ~/.ssh/id_rsa_key_2

  10. How can I start ssh-agent on login?

    • Use systemd by adding a user systemd unit for ssh-agent.
    • See start-ssh-agent-on-login on stackoverflow.

    • If you want to start ssh-agent on login, you have to add a ssh-agent.service user systemd unit, export SSH_AUTH_SOCK environment in the .bashrc file, enable and start the ssh-agent unit, and specify (in the file ~/.ssh/config) that keys should be automatically added to a running ssh-agent.

    • file ~/.config/systemd/user/ssh-agent.service:

    [Unit]
Description=SSH key agent

[Service]
Type=forking
Environment=SSH_AUTH_SOCK=%t/ssh-agent.socket
ExecStart=/usr/bin/ssh-agent -a $SSH_AUTH_SOCK

[Install]
WantedBy=default.target
    1. file .bashrc:
    export SSH_AUTH_SOCK="$XDG_RUNTIME_DIR/ssh-agent.socket"
    1. in a terminal, run the commands:
    systemctl --user enable ssh-agent
systemctl --user start ssh-agent
    1. file ~./ssh/config, if you have two private keys:
    Host *
     AddKeysToAgent yes
     IdentityFile ~/.ssh/id_rsa_key_1
     IdentityFile ~/.ssh/id_rsa_key_2
    • Note that after login, before the first use of ssh (via ssh, git, …), your ssh-agent doesn't know about your keys, so ssh-add -l lists anything.

Servers

  1. How to run a php server?

    • Use php command.
    • php: PHP Command Line Interface.
    • If the directory contains a index.php file, to have the server running on localhost on port 8080, run the command:
    php -S localhost:8080

  2. How to run a server that automatically reload when files change on the system?

    • Use the command browser-sync.
    • See browsersync homepage.
    • If the directory contains an index.html file, to have the server reload each second, run the command:
    browser-sync start --reload-delay=1000 -w --server
    • If the browser tab doesn't refresh automatically when you modify files, then you have to add a snippet into your website, just before the closing </body> tag. If you run browser-sync start command line, this prints the snippet you have to add to your index.html file. When I did, this gave me that snippet:
    <script id="__bs_script__">//<![CDATA[
document.write("<script async src='http://HOST:3000/browser-sync/browser-sync-client.js?v=2.26.13'><\/script>".replace("HOST", location.hostname));
//]]></script>
    • If you want to install browser-sync, run the command:
    npm install -g browser-sync

  3. How can I rewrite apache rules?

    • Use RewriteCond and RewriteRule directives.
    • See module mod_rewrite from Apache documentation.

  4. How can I configure OVH config file on server?

  5. Where can I find good nginx resources?

  6. What does request URI refer to in nginx vocabulary?

    • The request URI is the part of the request that comes after the domain name or IP address/port.

  7. How can I install nginx on ubuntu?

    • Use apt and ufw command.
    • apt: high-level commandline interface for the package management system.
    • ufw: program for managing a netfilter firewall.
    • See install nginx by linuxize.
    • If you want to install nginx on ubuntu and get ready to use, update your packages with apt update, install it with apt install and open the ports used by nginx:
    sudo apt update
sudo apt install nginx
sudo ufw allow 'Nginx Full'
sudo ufw enable
    • If you want to check if nginx is running, run the command:
    sudo systemctl status nginx
    • Each time you modify your nginx configuration, you have to reload nginx. To do so, run the command:
    sudo systemctl reload nginx

  8. What is the default configuration of nginx after installing it?

    • See install nginx by linuxize.
    • By default, nginx serves the file index.nginx-debian.html on localhost (127.0.0.1) on port 80. Just after intalling nginx, before any modification, you can visit the address http://127.0.0.1 on your browser.
    • This happens because nginx looks at config files on the directory /etc/nginx/sites-enabled. It sees the file /etc/nginx/sites-enabled/default that is a symlink of the file /etc/nginx/sites-available/default. This default file tells nginx to serve the file index.nginx-debian.html that is in the directory /var/www/html. And the config file default, after flushing the commented lines, is as follow:
    server {
  listen 80 default_server;
  listen [::]:80 default_server;

  root /var/www/html;
  index index.html index.htm index.nginx-debian.html;
  server_name _;

  location / {
          # First attempt to serve request as file, then
          # as directory, then fall back to displaying a 404.
          try_files $uri $uri/ =404;
  }
}

  9. How can I set nginx to be a reverse proxy?

    • Use proxy_pass directive in your nginx block configuration.
    • To pass a request to an HTTP proxied server, the proxy_pass directive is specified inside a location.
    • See nginx reverse proxy by linuxize, reverse proxy from nginx.com and proxy_pass from nginx.org documentation.
    • If you want to serve at mydomain.com an application that is running as a http server (node app, flask app,…) on http://127.0.0.1:5000, your nginx block for mydomain.com defined in the file /etc/nginx/sites-available/mydomain.conf must contain the following lines:
    server {
  listen 80;
  server_name www.mydomain.com mydomain.com;

  location / {
  proxy_pass http://127.0.0.1:5000;
  }
}

  10. How can I fix the nginx error "error (nginx): cannot get /app" related to proxy servers?

    • See proxy_pass directive in your block configuration.
    • The error was that I was trying to pass location /app to the address http://127.0.0.1:5000 without putting a / a the end of the address.

    -To solve the problem, I add a / to the proxy_pass address. My block configuration /etc/nginx/sites-available/mydomain.conf contains know the following lines:

    location /app {
  proxy_pass http://127.0.0.1:5000/;
}

Connection

  1. How can I restart my wifi connection?

    • Use service command.
    • service: run a System V init script.
    • See restart wifi connection on askubuntu.
    • If you want to restart your wifi connection, run the command:
    sudo service network-manager restart

  2. How can I check if I'm connected to a wireless network?

    • Use iwgetid command.
    • iwgetid: report ESSID, NWID or AP/Cell Address of wireless network.
    • If you want to check if you are connected to a wireless newtork, run the following command and if you get nothing, you are not connected:
    iwgetid

ftp

  1. Why do I get kicked out of a FTP session once I run a command?

    • Use ufw command.
    • ufw: program for managing a netfilter firewall.
    • See ftp error due to firewall on stackexchange.
    • If you want to open all the port to not have problem of firewall with ftp, run the command:
    sudo ufw disable

  2. What ftp command is for?

    • ftp is an internet file transfer program.

Miscellaneous

  1. What curl command is for?

    • curl: transfer a URL.

  2. What wget command is for?

    • wget: the non-interactive network downloader.

  3. What ping command is for?

    • ping: send ICMP ECHO_REQUEST to network hosts.

Package management

Linux packages

  1. How can I list linux packages related to a regexp?

    • Use apt-cache search command.
    • apt-cache search: perform a full text search on all available package lists for the POSIX regex pattern given.
    • If you want to search linux packages related to emacs, run the command:
    apt-cache search emacs

  2. How can I show linux package information?

    • Use apt-cache show command.
    • apt-cache show: display the package records for the named packages.
    • If you want to show the information of the installed emacs package, run the command:
    apt-cache show emacs

  3. How can I update the list of available linux packages?

    • Use apt-get update command.
    • apt-get update: this command is used to resynchronize the package index files from their sources.

  4. How can I list the installed packages?

    • Use apt list command.
    • apt list: list package satifying certain criteria.
    • See list installed packages by linuxize.
    • If you want to list all installed packages, run the command:
    apt list --installed
    • If you want to check if the package emacs is installed, run the command:
    apt list --installed | grep emacs

  5. How can I install newest versions of all my packages?

    • Use apt-get upgrade command.
    • This command installs the newest versions of all packages currently installed on the system from the sources enumerated in etc/apt/sources.list file.

  6. How can I install a new linux package?

    • Use apt-get install command.
    • apt-get install: install new one or more linux packages.
    • If you want to install emacs, run the command:
    apt-get install emacs

  7. How can I remove a linux package?

    • Use apt-get remove command.
    • apt-get remove: remove linux packages. Note that removing a package leaves its configuration files on the system.
    • If you want to remove emacs, run the command:
    apt-get remove emacs

  8. How can I get the list of the libraries a command depends on?

    • Use ldd command.
    • ldd: print shared object dependencies.
    • If you want to list the library dependencies of the ls command, run the command:
    ldd /bin/ls
    • On my computer the previous command gave me:
    linux-vdso.so.1 (0x00007ffeeb143000)
libselinux.so.1 => /lib/x86_64-linux-gnu/libselinux.so.1 (0x00007f2203fc5000)
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f2203bd4000)
libpcre.so.3 => /lib/x86_64-linux-gnu/libpcre.so.3 (0x00007f2203962000)
libdl.so.2 => /lib/x86_64-linux-gnu/libdl.so.2 (0x00007f220375e000)
/lib64/ld-linux-x86-64.so.2 (0x00007f220440f000)
libpthread.so.0 => /lib/x86_64-linux-gnu/libpthread.so.0 (0x00007f220353f000)

npm for nodejs

  1. How can I list the the nodejs installed packages?

    • Use ls subcommand of npm.
    • npm ls: Print packages' version that are installed, as well as their dependencies, in a tree-structure.
    • If you want to list the installed packages in your node project, in root directory of your project run the command:
    npm ls
    • If you want to list the node installed packages globaly in your machine, run the command:
    npm ls -g
    • If you want to list only the name@version of the installed packages in your node project, you have to limite the depth of the printed tree. To do so, run the command:
    npm ls -g --depth=0

pip for python

  1. What is pip?

    • pip is a package installer for python. You can use pip to install packages from the Python Package Index and other indexes.
    • See pip on pypi.

brew for missing packages on macOS

  1. How can I install brew?

    • See brew homepage.
    • To install brew, run the command:
    /bin/bash -c "$(curl -fsSL \
  https://raw.githubusercontent.com/Homebrew/install/master/install.sh)"

nix

  1. What is nix?

Process and system

pm2

  1. How can I install pm2?

    • Use npm command.
    • npm: javascript package manager.
    • If you want to install pm2 globaly, run the command:
    npm install pm2 -g
    • If you want to start your app.js application, run the command:
    pm2 start app.js

  2. How can I start and daemonize applications with pm2?

    • Use pm2 start command.
    • pm2 start: start and daemonize an app.
    • See quick start from the documentation.
    • If you want to start and daemonize with pm2 your application that normally start by running npm start, run the command:
    pm2 start npm -- start
    • If you want to start and daemonize with pm2 your application that normally start by running npm start -- --port=5000, run the command:
    pm2 start npm -- start --port=5000
    • If you want to start and daemonize with pm2 your application that normally start by running npm start and give it the name my-app run the command:
    pm2 start npm --name my-app -- start

  3. How can I automatically restart application on boot/reboot?

    • Use pm2 startup and pm2 save commands.
    • pm2 startup: enable the pm2 startup hook.
    • pm2 save: freeze a process list for automatic respawn.
    • See quick start from the documentation.
    • If you want that pm2 automatically restart on boot/reboot and run the saved processes, you have to enable the pm2 startup hook and freeze a list of the current running processes. To do so, run the commands:
    pm2 startup  #then copy/past and run the generated command
pm2 save
    • If you want to revert the action pm2 startup, run the command:
    pm2 unstartup  #then copy/past and run the generated command

  4. What are the common actions I want to do with pm2?

    • See documentation and pm2 --help.
    • List of commands, without description:
    pm2 example
pm2 list
pm2 show <name|id>
pm2 stop <name|id>
pm2 delete <name|id>
pm2 restart <name|id>
pm2 status
pm2 start
pm2 logs
    • List of options, without description: --watch, --ignore-watch, --watch-delay.

CPU

  1. How can I know the caracteristics of my CPU?

    • Use lscpu command.
    • lscpu: display information about the CPU architecture.
    • See number of cores of as system on stackexchange.
    • If you want to know how many physical CPU do you have, run the command lscpu and see the line which starts with Socket(s):.
    • If you want to know how many core per socket do you have, run the command lscpu and see the line which starts with CPU(s):.
    • After running the command lscpu, I get this output:
    Architecture:        x86_64
CPU op-mode(s):      32-bit, 64-bit
Byte Order:          Little Endian
CPU(s):              4
On-line CPU(s) list: 0-3
Thread(s) per core:  2
Core(s) per socket:  2
Socket(s):           1
NUMA node(s):        1
Vendor ID:           GenuineIntel
CPU family:          6
Model:               69
Model name:          Intel(R) Core(TM) i5-4300U CPU @ 1.90GHz
Stepping:            1
CPU MHz:             1046.894
CPU max MHz:         2900.0000
CPU min MHz:         800.0000
BogoMIPS:            4988.47
Virtualization:      VT-x
L1d cache:           32K
L1i cache:           32K
L2 cache:            256K
L3 cache:            3072K
NUMA node0 CPU(s):   0-3
Flags:               fpu vme de pse tsc msr pae mce cx8 apic sep
mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss
ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc arch_perfmon
pebs bts rep_good nopl xtopology nonstop_tsc cpuid aperfmperf pni
pclmulqdq dtes64 monitor ds_cpl vmx smx est tm2 ssse3 sdbg fma cx16
xtpr pdcm pcid sse4_1 sse4_2 x2apic movbe popcnt tsc_deadline_timer
aes xsave avx f16c rdrand lahf_lm abm cpuid_fault epb invpcid_single
pti ssbd ibrs ibpb stibp tpr_shadow vnmi flexpriority ept vpid ept_ad
fsgsbase tsc_adjust bmi1 avx2 smep bmi2 erms invpcid xsaveopt dtherm
ida arat pln pts md_clear flush_l1d

hardware

  1. How can I get the characteristics of my RAM?

    • Use lshw command.
    • lshw: extract detailed information on the hardware configuration of the machine.
    • See frequency and type of my current RAM on askubuntu.
    • If you want to get characteristics of your RAM, run the command:
    sudo lshw -C memory
    • After running the previous command, I got this output:
    *-firmware
     description: BIOS
     vendor: Hewlett-Packard
     physical id: c
     version: L71 Ver. 01.07
     date: 02/09/2014
     size: 64KiB
     capacity: 8128KiB
     capabilities: pci pcmcia upgrade shadowing
     cdboot bootselect edd int5printscreen int9keyboard
     int14serial int17printer acpi usb smartbattery
     biosbootspecification netboot uefi
*-cache:0
     description: L1 cache
     physical id: 2
     slot: Unknown
     size: 32KiB
     capacity: 32KiB
     capabilities: asynchronous internal write-back instruction
     configuration: level=1
*-cache:1
     description: L2 cache
     physical id: 3
     slot: Unknown
     size: 256KiB
     capacity: 256KiB
     capabilities: asynchronous internal write-back unified
     configuration: level=2
*-cache:2
     description: L3 cache
     physical id: 4
     slot: Unknown
     size: 3MiB
     capacity: 3MiB
     capabilities: asynchronous internal write-back unified
     configuration: level=3
*-cache
     description: L1 cache
     physical id: 1
     slot: Unknown
     size: 32KiB
     capacity: 32KiB
     capabilities: asynchronous internal write-back data
     configuration: level=1
*-memory
     description: System Memory
     physical id: 7
     slot: System board or motherboard
     size: 4GiB
   *-bank:0
        description: SODIMM DDR3 Synchronous 1600 MHz (0.6 ns)
        product: HMT351S6EFR8A-PB
        vendor: Hynix/Hyundai
        physical id: 0
        serial: 00821224
        slot: Bottom-Slot 1(left)
        size: 4GiB
        width: 64 bits
        clock: 1600MHz (0.6ns)
   *-bank:1
        description: DIMM [empty]
        physical id: 1
        slot: Bottom-Slot 2(right)

  2. How can I list the hardwares of my system?

    • Use lshw command.
    • lshw: extract detailed information on the hardware configuration of the machine.
    • I you want to list the hardwares of your system, run the command:
    sudo lshw -short
    • After running the previous command, I got this output:
    H/W path         Device     Class          Description
======================================================
                            system         HP EliteBook 840 G1 (F9X37UP#ABF)
/0                          bus            198F
/0/c                        memory         64KiB BIOS
/0/0                        processor      Intel(R) Core(TM) i5-4300U CPU @ 1.90GHz
/0/0/2                      memory         32KiB L1 cache
/0/0/3                      memory         256KiB L2 cache
/0/0/4                      memory         3MiB L3 cache
/0/1                        memory         32KiB L1 cache
/0/7                        memory         4GiB System Memory
/0/7/0                      memory         4GiB SODIMM DDR3 Synchronous 1600 MHz (0.6 ns)
/0/7/1                      memory         DIMM [empty]
/0/100                      bridge         Haswell-ULT DRAM Controller
/0/100/2                    display        Haswell-ULT Integrated Graphics Controller
/0/100/3                    multimedia     Haswell-ULT HD Audio Controller
/0/100/14                   bus            8 Series USB xHCI HC
/0/100/14/0      usb2       bus            xHCI Host Controller
/0/100/14/0/3               bus            USB2134B
/0/100/14/0/3/3             input          USB OPTICAL MOUSE
/0/100/14/0/3/4             input          USB Keyboard
/0/100/14/0/5               generic        VFS495 Fingerprint Reader
/0/100/14/0/7               multimedia     HP HD Webcam
/0/100/14/1      usb3       bus            xHCI Host Controller
/0/100/14/1/3               bus            USB5534B
/0/100/16                   communication  8 Series HECI #0
/0/100/16.3                 communication  8 Series HECI KT
/0/100/19        enp0s25    network        Ethernet Connection I218-LM
/0/100/1b                   multimedia     8 Series HD Audio Controller
/0/100/1c                   bridge         8 Series PCI Express Root Port 1
/0/100/1c.3                 bridge         8 Series PCI Express Root Port 4
/0/100/1c.3/0    wlo1       network        Wireless 7260
/0/100/1c.5                 bridge         8 Series PCI Express Root Port 6
/0/100/1c.5/0               generic        RTS5227 PCI Express Card Reader
/0/100/1d                   bus            8 Series USB EHCI #1
/0/100/1d/1      usb1       bus            EHCI Host Controller
/0/100/1d/1/1               bus            USB hub
/0/100/1f                   bridge         8 Series LPC Controller
/0/100/1f.2                 storage        8 Series SATA Controller 1 [AHCI mode]
/0/100/1f.3                 bus            8 Series SMBus Controller
/0/2             scsi0      storage
/0/2/0.0.0       /dev/sda   disk           180GB INTEL SSDSC2BF18
/0/2/0.0.0/1     /dev/sda1  volume         167GiB EXT4 volume
/1                          power          CM03050XL

  3. What is dual channel memory?

  4. How to upgrade my pc RAM?

systemd

  1. How do I reload the configuration file of a systemd unit?

    • Use daemon-reload subcommand of systemctl.
    • systemctl daemon-reload: reload the systemd manager configuration.
    • If you want your changes in myservice.service systemd unit file to be reload, run the command:
    systemctl daemon-reload

  2. What is systemd?

    • systemd: a system and service manager for Linux operating systems.

  3. What systemctl command is for?

    • systemctl: control the systemd system and service manager.
    • See systemd from Archlinux wiki.
    • Common command lines using systemctl:
    systemctl list-unit-files --user
systemctl show --property MainPID --value emacs --user
systemctl status emacs --user

  4. What journalctl command is for?

    • journalctl: Query the systemd journal.

ps command

  1. What ps command is for?

    • ps: report a snapshot of the current processes.

  2. What does STAT column refer to in the output of ps command?

    • This column indicate the process states.
    • See stackexchange.
    • If I run the command ps -x, the first 8 lines of the output I get are:
    PID TTY      STAT   TIME COMMAND
1104 ?        Ssl    0:00 PM2 v4.2.3: God Daemon (/home/tony/.pm2)
1647 ?        Ss     0:01 /lib/systemd/systemd --user
1648 ?        S      0:00 (sd-pam)
1663 ?        Ss     0:00 /usr/bin/ssh-agent -a /run/user/1000/ssh-agent.socket
1670 tty2     Ssl+   0:00 /usr/lib/gdm3/gdm-x-session --run-script i3
1672 tty2     Sl+    1:18 /usr/lib/xorg/Xorg vt2 -displayfd 3 -auth /run/user/1
1687 ?        Ss     0:00 /usr/bin/dbus-daemon --session --address=systemd: --n
1690 tty2     S+     0:01 i3
    • Processes states that ps indicates are:
    D Uninterruptible sleep (usually IO)
R Running or runnable (on run queue)
S Interruptible sleep (waiting for an event to complete)
T Stopped, either by a job control signal or because it is being traced.
W paging (not valid since the 2.6.xx kernel)
X dead (should never be seen)
Z Defunct ("zombie") process, terminated but not reaped by its parent.
    • and the additional characters are:
    < high-priority (not nice to other users)
N low-priority (nice to other users)
L has pages locked into memory (for real-time and custom IO)
s is a session leader
l is multi-threaded (using CLONE_THREAD, like NPTL pthreads do)
+ is in the foreground process group

  3. What does TTY mean in the command ps?

    • A TTY is a computer terminal. In the context of ps, it is the terminal that executed a particular command.
    • The abbreviation stands for TeleTYpewriter, which were devices that allowed users to connect to early computers.
    • See stackoverflow.

socket

  1. What is a socket?

    • A Unix domain socket or IPC socket is a data communications endpoint for exchanging data between processes executing on the same host operating system.
    • See wikipedia and stackexchange.

  2. Where is my emacs server socket?

    • In the directory /var/run/user/1000/emacs/.

miscellaneous

  1. What hostnamectl command is for?

    • hostnamectl: control the system hostname.

  2. What top command is for?

    • top: display Linux processes.

  3. How can I check the PID number of my emacs process?

    pidof emacs

Scripts

Makefile

  1. Where can I find a good tutorial on Makefile?

  2. What is a Makefile?

  3. How to use wildcard in Makefile?

    • Use the function wildcard of the make syntax.
    • See wildcard in makefile on stackoverflow.
    • If you have two source files foo.c and bar.c, to set the value of the variable programs with foo.c bar.c, add this line to your Makefile:
    programs:=$(wildcard *.c)

bash script

  1. Where can I find a good cheatsheet about bash scripting?

  2. How can I know the status of the last command run in my terminal?

    • Use $? symbol and echo command.
    • echo: display a line of text.
    • See bash functions.
    • If you want to print the status of the last command run in your terminal, run the command:
    echo $?
    • When a bash function completes, its return value is the status of the last statement executed in the function, 0 for success and non-zero decimal number in the 1 - 255 range for failure.

Format outputs

  1. How can I format numbers in bash script?

    • Use printf command.
    • printf: format and print data.
    • See formatting numerical output in bash.
    • If you want to transform 12.3 to 12 and 3.62 to 03, the printf format to use is %02.0f. So, running the following command gives you the expected results:
    printf "%02.0f" 12.3
printf "%02.0f" 3.62

UI

GTK

  1. How to make chromium using GTK?

    • If you want that chromium uses GTK, in chromium allow GTK+ theme in: Settings > Preferences > Appearence > Use GTK+ theme.

  2. What are the GTK config files?

    • ~/.gtkrc-2.0 for gtk2,
    • ~/.config/gtk-3.0/settings.ini for gtk-3,
    • /etc/gtk-3.0/settings.ini.

  3. How to get information on the GTK settings?

    • Run the command:
    gtk-query-settings

  4. Where are stored the GTK themes?

    • You can find GTK themes in the directory: /usr/share/themes/.

  5. How can I add emacs like keybinding in GTK applications like chromium?

    • In gtk-2 add the line in your GTK config file /.gtkrc-2.0.
    gtk-key-theme-name = "Emacs"
    • In gtk-3, add the following line in your GTK config file /.config/gtk-3.0/settings.ini.
    gtk-key-theme-name = Emacs

  6. Where the emacs like keybinding in GTK applications are defined?

    • In gtk-2, the implemented emacs keybinding can be found in the file /usr/share/themes/Emacs/gtk-2.0-key/gtkrc:
    #
# Bindings for GtkTextView and GtkEntry
#
binding "gtk-emacs-text-entry"
{
  bind "<ctrl>b" { "move-cursor" (logical-positions, -1, 0) }
  bind "<shift><ctrl>b" { "move-cursor" (logical-positions, -1, 1) }
  bind "<ctrl>f" { "move-cursor" (logical-positions, 1, 0) }
  bind "<shift><ctrl>f" { "move-cursor" (logical-positions, 1, 1) }

  bind "<alt>b" { "move-cursor" (words, -1, 0) }
  bind "<shift><alt>b" { "move-cursor" (words, -1, 1) }
  bind "<alt>f" { "move-cursor" (words, 1, 0) }
  bind "<shift><alt>f" { "move-cursor" (words, 1, 1) }

  bind "<ctrl>a" { "move-cursor" (paragraph-ends, -1, 0) }
  bind "<shift><ctrl>a" { "move-cursor" (paragraph-ends, -1, 1) }
  bind "<ctrl>e" { "move-cursor" (paragraph-ends, 1, 0) }
  bind "<shift><ctrl>e" { "move-cursor" (paragraph-ends, 1, 1) }

  bind "<ctrl>w" { "cut-clipboard" () }
  bind "<ctrl>y" { "paste-clipboard" () }

  bind "<ctrl>d" { "delete-from-cursor" (chars, 1) }
  bind "<alt>d" { "delete-from-cursor" (word-ends, 1) }
  bind "<ctrl>k" { "delete-from-cursor" (paragraph-ends, 1) }
  bind "<alt>backslash" { "delete-from-cursor" (whitespace, 1) }

  bind "<alt>space" { "delete-from-cursor" (whitespace, 1)
                      "insert-at-cursor" (" ") }
  bind "<alt>KP_Space" { "delete-from-cursor" (whitespace, 1)
                         "insert-at-cursor" (" ")  }

  #
  # Some non-Emacs keybindings people are attached to
  #
  bind "<ctrl>u" {
     "move-cursor" (paragraph-ends, -1, 0)
     "delete-from-cursor" (paragraph-ends, 1)
  }
  bind "<ctrl>h" { "delete-from-cursor" (chars, -1) }
  bind "<ctrl>w" { "delete-from-cursor" (word-ends, -1) }
}

#
# Bindings for GtkTextView
#
binding "gtk-emacs-text-view"
{
  bind "<ctrl>p" { "move-cursor" (display-lines, -1, 0) }
  bind "<shift><ctrl>p" { "move-cursor" (display-lines, -1, 1) }
  bind "<ctrl>n" { "move-cursor" (display-lines, 1, 0) }
  bind "<shift><ctrl>n" { "move-cursor" (display-lines, 1, 1) }

  bind "<ctrl>space" { "set-anchor" () }
  bind "<ctrl>KP_Space" { "set-anchor" () }
}

#
# Bindings for GtkTreeView
#
binding "gtk-emacs-tree-view"
{
  bind "<ctrl>s" { "start-interactive-search" () }
  bind "<ctrl>f" { "move-cursor" (logical-positions, 1) }
  bind "<ctrl>b" { "move-cursor" (logical-positions, -1) }
}

#
# Bindings for menus
#
binding "gtk-emacs-menu"
{
  bind "<ctrl>n" { "move-current" (next) }
  bind "<ctrl>p" { "move-current" (prev) }
  bind "<ctrl>f" { "move-current" (child) }
  bind "<ctrl>b" { "move-current" (parent) }
}

class "GtkEntry" binding "gtk-emacs-text-entry"
class "GtkTextView" binding "gtk-emacs-text-entry"
class "GtkTextView" binding "gtk-emacs-text-view"
class "GtkTreeView" binding "gtk-emacs-tree-view"
class "GtkMenuShell" binding "gtk-emacs-menu"
    • In gtk-3, the implemented emacs keybinding can be found in the file /usr/share/themes/Emacs/gtk-3.0/gtk-keys.css.
    /*
 * Bindings for GtkTextView and GtkEntry
 */
@binding-set gtk-emacs-text-entry
{
  bind "<ctrl>b" { "move-cursor" (logical-positions, -1, 0) };
  bind "<shift><ctrl>b" { "move-cursor" (logical-positions, -1, 1) };
  bind "<ctrl>f" { "move-cursor" (logical-positions, 1, 0) };
  bind "<shift><ctrl>f" { "move-cursor" (logical-positions, 1, 1) };

  bind "<alt>b" { "move-cursor" (words, -1, 0) };
  bind "<shift><alt>b" { "move-cursor" (words, -1, 1) };
  bind "<alt>f" { "move-cursor" (words, 1, 0) };
  bind "<shift><alt>f" { "move-cursor" (words, 1, 1) };

  bind "<ctrl>a" { "move-cursor" (paragraph-ends, -1, 0) };
  bind "<shift><ctrl>a" { "move-cursor" (paragraph-ends, -1, 1) };
  bind "<ctrl>e" { "move-cursor" (paragraph-ends, 1, 0) };
  bind "<shift><ctrl>e" { "move-cursor" (paragraph-ends, 1, 1) };

  /* bind "<ctrl>w" { "cut-clipboard" () }; */
  bind "<ctrl>y" { "paste-clipboard" () };

  bind "<ctrl>d" { "delete-from-cursor" (chars, 1) };
  bind "<alt>d" { "delete-from-cursor" (word-ends, 1) };
  bind "<ctrl>k" { "delete-from-cursor" (paragraph-ends, 1) };
  bind "<alt>backslash" { "delete-from-cursor" (whitespace, 1) };

  bind "<alt>space" { "delete-from-cursor" (whitespace, 1)
                      "insert-at-cursor" (" ") };
  bind "<alt>KP_Space" { "delete-from-cursor" (whitespace, 1)
                         "insert-at-cursor" (" ")  };
  /*
   * Some non-Emacs keybindings people are attached to
   */
  bind "<ctrl>u" { "move-cursor" (paragraph-ends, -1, 0)
                   "delete-from-cursor" (paragraph-ends, 1) };

  bind "<ctrl>h" { "delete-from-cursor" (chars, -1) };
  bind "<ctrl>w" { "delete-from-cursor" (word-ends, -1) };
}

/*
 * Bindings for GtkTextView
 */
@binding-set gtk-emacs-text-view
{
  bind "<ctrl>p" { "move-cursor" (display-lines, -1, 0) };
  bind "<shift><ctrl>p" { "move-cursor" (display-lines, -1, 1) };
  bind "<ctrl>n" { "move-cursor" (display-lines, 1, 0) };
  bind "<shift><ctrl>n" { "move-cursor" (display-lines, 1, 1) };

  bind "<ctrl>space" { "set-anchor" () };
  bind "<ctrl>KP_Space" { "set-anchor" () };
}

/*
 * Bindings for GtkTreeView
 */
@binding-set gtk-emacs-tree-view
{
  bind "<ctrl>s" { "start-interactive-search" () };
  bind "<ctrl>f" { "move-cursor" (logical-positions, 1) };
  bind "<ctrl>b" { "move-cursor" (logical-positions, -1) };
}

/*
 * Bindings for menus
 */
@binding-set gtk-emacs-menu
{
  bind "<ctrl>n" { "move-current" (next) };
  bind "<ctrl>p" { "move-current" (prev) };
  bind "<ctrl>f" { "move-current" (child) };
  bind "<ctrl>b" { "move-current" (parent) };
}

entry {
  -gtk-key-bindings: gtk-emacs-text-entry;
}

textview {
  -gtk-key-bindings: gtk-emacs-text-entry, gtk-emacs-text-view;
}

treeview {
  -gtk-key-bindings: gtk-emacs-tree-view;
}

GtkMenuShell {
  -gtk-key-bindings: gtk-emacs-menu;
}

  7. How to switch between GTK themes?

    • Use gtk-theme-switch command.
    • To install it, run the command:
    sudo apt install gtk-theme-switch

  8. How to modify text size of GTK applications like chromium?

    • In gtk-3, add the following line in your GTK config file /.config/gtk-3.0/settings.ini.
    gtk-font-name=Sans 12

  9. How can I find GTK resources?

  10. How can I test/debug components of an application that uses GTK for the UI?

    • Use GTK inspector.
    • See GTK inspector on gnome.org.
    • To do so, run the command:
    GTK_DEBUG=interactive <app-name>
    • To install GTK inspector, you have to install the package

    libgtk-3-dev, to do so, run the command:

    sudo apt install libgtk-3-dev

Xft

  1. How can I scale up my screen view?

    • Use ~/.Xresources file and/or xrdb command.
    • Many desktop environments use xrdb to load ~/.Xresources files on session startup to initialize the resource database.
    • See Xresources and HiDPX archlinux.
    • If you want to scale up what you see on your screen, saying that your dpi (dot per inch) is equal to 96 and you want to raise up to 144 dpi (dpi must be a multiple of 96), you can add this line Xft.dpi: 144 to the file ~/.Xresources, and run the command:
    xrdb -merge ~/.Xresources
    • If you want to check the currently loaded resources, run the command:
    xrdb -query all
    • To see the default settings of your installed X11 apps, look in /etc/X11/app-defaults/.

i3 window manager

  1. How can I debug i3status and i3blocks config files?

    • Use i3status or i3bloks commands.
    • i3blocks: a flexible scheduler for your i3bar blocks.
    • i3status: generates a status line for i3bar.
    • If you want to debug i3status config file, run the command:
    i3status ~/config/i3/config
    • If you want to debug i3blocks config file, run the command:
    i3blocks -c ~/.config/i3blocks/config

  2. How can I know the key name use by i3 config file for a specific key?

    • Use xev command.
    • xev: print contents of X events.
    • If you want to get information about a specific key on your keyboard, that you can use in your i3 config file, run the command xev in your terminal, a (Event tester) window popup, then press the key from which you want to get information. For instance, pressing the space key on my keyboard, I get this following output where keycode 65 (keysym 0x20, space) is the interesting part and the name to use in i3 config file is space.
    KeyRelease event, serial 34, synthetic NO, window 0x1400001,
    root 0x14f, subw 0x0, time 713381482, (524,452), root:(528,472),
    state 0x0, keycode 65 (keysym 0x20, space), same_screen YES,
    XLookupString gives 1 bytes: (20) " "
    XFilterEvent returns: False

Gnome

  1. How can I reset all gnome settings?

    • Use gnome-tweaks command.
    • gnome-tweaks: customize your Ubuntu Gnome desktop.
    • If you want to reset all gnome desktop settings to default, launch gnome-tweak and in its gnome menu click Reset to Defaults.
    • if you want to install gnome-tweaks, run the command:
    sudo apt install gnome-tweaks

  2. How can I modify the text size on Gnome desktop?

    • Use gsettings command.
    • gsettings: GSettings configuration tool.
    • See example find and change the screen dpi on askubuntu.
    • If you want to change the dpi in Ubuntu Gnome desktop, you can't because it's hard coded to a value of 96 dpi. But you can change the text size of the applications. For instance, to increase the text size by 1.2 (of the hard coded 96 dpi, i.e. 1.2*96), set to 1.2 the value of the key text-scaling-factor of the shema org.gnome.desktop.interface run the command:
    gsettings set org.gnome.desktop.interface text-scaling-factor 1.2
    • If you want to go back to the default text size, reset the value of key text-scaling-factor. To do so, run the command:
    gsettings reset org.gnome.desktop.interface text-scaling-factor

fonts

  1. How can I list all available font on my system?

    • Use fc-list command.
    • fc-list: list available fonts.
    • If you want to list all available font, run the command:
    fc-list
    • Note: the font symbola allow you to print all unicode character.

Users and groups

Sudo and Root

  1. How can I switch to root user?

    • Use su command.
    • su: change user ID or become superuser.
    • See su command by linuxize.
    • If you want to run an interactive shell as root when root's password is already defined, run the command:
    su
    • If you want to run an interactive shell as root when root's password is not defined, run the command:
    sudo su -

  2. How can I add a user to the sudo group?

    • Use usermod command.
    • usermod: modify a user account.
    • If you want to add the user jim to the group sudo, run the command:
    sudo usermod -aG sudo jim

  3. How can I remove a user from the sudo group?

    • Use deluser command.
    • deluser: remove a user from the system.
    • If you want to remove the user jim from the group sudo, run the command:
    sudo deluser jim sudo

  4. How can I modify the sudo password timeout?

    • Use visudo command.
    • visudo: edit the sudoers file in a safe fashion.
    • See sudo password timeout by maketecheasier.
    • If you want to change the default (15mins) sudo password timeout to 30mins, change the line Defaults env_reset to the line Defaults env_reset, timestamp_timeout=30 in the file /etc/sudoers, not directly, but by running the command:
    sudo visudo
    • If you want to check the existing sudoers file for syntax errors and mode, run the command:
    sudo visudo -c
    • If you want that the system prompt you for password everytime you use sudo, set the sudo password timeout to 0, by changing the line Defaults env_reset to the line Defaults env_reset, timestamp_timeout=0 in the file /etc/sudoers, not directly, but by running the command:
    sudo visudo

Groups

  1. How can I list all groups a user is a member of?

    • Use groups command.
    • groups: print the groups a user is in.
    • See how to list groups in linux by linuxize.
    • If you want to list the groups the user jim is a member of, run the command:
    groups jim
groups # if you're logged as jim

  2. How can I list all groups present on the system?

    • Use getent command.
    • getent: get entries from Name Service Switch libraries.
    • See how to list groups in linux by linuxize.
    • If you want to list all groups present on the system, run the command:
    getent group

Passwords

  1. How can I enable root user account?

    • Use passwd command.
    • passwd: change user password.
    • See root user account by linuxize.
    • If you want to enable the root user account and you have the sudo privileges, run the command:
    sudo passwd root
    • If you want to disable the root user account and you have the sudo privileges, run the command:
    sudo passwd -l root

  2. How can I encrypt a password that can be used in the /etc/shadow file?

    • Use mkpasswd command.
    • mkpasswd: Encrypts the given password with the crypt(3) libc function using the given salt.
    • See examples generate a password in shadow file on stackexchange.
    • If you want to encrypt a password into SHA 512 hash with the given salt saltsalt, run the command (and type your password):
    mkpasswd -m sha-512 -S saltsalt
    • If you want to encrypt a password into SHA 512 hash without specifying the salt (a random one will be provide), run the command (and type your password):
    mkpasswd -m sha-512
    • I you want to list all the encryption methods, run the command:
    mkpasswd -m help
    • I you want to install the mkpasswd command, you have to install the package whois. To do so, run the command:
    sudo apt install whois

UID

  1. How can I modify the UID of an user on linux?

    • Use usermod command.
    • usermod: modify a user account.
    • See usermod command example by linuxize.
    • If you want to modify the UID of the user tony to the number 1050 for instance, run the command:
    usermod -u 1050 tony
    • If you want to print the UID of the user tony, run the command:
    id tony
id   # if you're logged as tony

Miscellaneous

  1. What adduser command is for?

    • adduser: add a user to the system.

  2. What addgroup command is for?

    • addgroup: add a group to the system.

  3. What delgroup command is for?

    • delgroup: remove a user from the system.

  4. What chown command is for?

    • chown: change file owner and group.

  5. What chgrp command is for?

    • chgrp: change group ownership.

X window system

Get X information

  1. How can I print all X information on a selected window?

    • Use xwininfo command.
    • xwininfo: window information utility for X.
    • If you want to to print all X information on a selected window, run the command xwininfo -all and click on the window you want the information from:
    xwininfo -all  # and click on the window you want the information from

X and i3

  1. How can I kill a window that I can't kill with i3?

    • Use xkill command.
    • xkill: kill a client by its X resource.
    • If you want to kill a window that doesn't respond, run the command xkill and click on the window you want to kill:
    xkill  # and click on the window you want to kill

  2. How can I get the instance and class of X window that are used with i3?

    • Use xprop command.
    • xprop: property displayer for X.
    • If you want to get the instance and class of an X window in order to use them with i3, run the command xprop and click on the window you want the information from and inspect the line starting by WM_CLASS(STRING):.
    xprop  # and click on the window you want the information from
    • For example with a window running chromium-browser application, I get the following line where chromium-browser is the instance, second Chromium-browser is the class:
    WM_CLASS(STRING) = "chromium-browser", "Chromium-browser"

Multiple monitors

  1. How can I display a monitor on the left of the other monitor?

    • Use xrandr command.
    • xrandr: set the size, orientation and/or reflection of the outputs for a screen.
    • If you want to display the monitor DP-2 on the left of the monitor eDP-1, run the command:
    xrandr --output DP-2 --left-of eDP-1
    • If you want to get the names of the outputs you want to display with xrandr, run the command xrandr and seek for lines like those ones (in my case eDP-1 and DP-2 are the monitors I want to display side by side):
    eDP-1 connected primary 1366x768+0+0 (normal left inverted right x axis y axis) 309mm x 173mm
DP-2 connected 1280x1024+1366+0 (normal left inverted right x axis y axis) 338mm x 270mm

Miscellaneous

  1. What xbindkey command is for?

    • xbindkey: a grabbing keys program for X.

  2. What xmodmap command is for?

    • xmodmap: utility for modifying keymaps and pointer button mappings in X.

  3. How can I list the open windows?

    • Use wmctrl command.
    • wmctrl: interact with a EWMH/NetWM compatible X Window Manager.
    • If you want to list the windows being managed by the window manager, run the command:
    wmctrl -l

  4. How can I simulate a key plus mouse click from commande line?

    • Use xdotool command.
    • xdotool: command-line X11 automation tool.
    • See simultaneous key + mouse click on stackoverflow and xdotool man page on ubuntu.
    • If you want to simulate alt+mouse-1 simultaneously from command line, run the command:
    xdotool keydown alt click 1 keyup alt

  5. How can I get current mouse coordinates from bash?

    • Use xdotool command.
    • xdotool: command-line X11 automation tool.
    • See get current mouse coordinates on stackoverflow.
    • If you want to get the current mouse coordinates location from command line, run the command:
    xdotool getmouselocation
    • If you want to get the current mouse coordinates location and set the variables X and Y to hold respectively the horizontal and vertical position, run the command:
    eval $(xdotool getmouselocation --shell)

  6. Some use cases of xdotool command

    • If I run the command xdotool getactivewindow I get 27263352.
    • If I run the command xdotool getactivewindow getwindowname from my terminal I get Terminal.
    • If I run the command xdotool getactivewindow | xprop -id 27263352 WM_CLASS, I got this output:
    WM_CLASS(STRING) = "gnome-terminal-server", "Gnome-terminal"

Autokey

  1. How can I install autokey?

    • Use git and pip3 commands.
    • pip3: a tool for installing and managing Python packages.
    • git: the stupid content tracker.
    • See Installing wiki and PyGObject getting started documentation.
    • If you want to install autokey with pip3, clone the repository, install dependencies that are not in setup.py files as wheel, dbus-python and PyGObject, and, install autokey from the cloned repository. We do every needed steps in a python virtual environment. Finally, we make a symlink of autokey-gtk executable in ~/.local/bin/ directory to be able to use autokey widely without activating the python virtual environment. To do so, we run the commands:
    $ git clone https://github.com/autokey/autokey.git
$ cd autokey
$ python3 -m venv ~/.py-venv/autokey/
$ source ~/.py-venv/autokey/bin/activate
(autokey) $ pip3 install wheel dbus-python
(autokey) $ sudo apt install libgirepository1.0-dev gcc \
            libcairo2-dev pkg-config python3-dev gir1.2-gtk-3.0 \
            # for PyGObject
(autokey) $ pip3 install pycairo
(autokey) $ pip3 install PyGObject
(autokey) $ pip3 install .
(autokey) $ ln -s ~/.py-venv/autokey/bin/autokey-gtk \
            ~/.local/bin/autokey-gtk
(autokey) $ deactivate
    • To start autokey with the GUI, run the command:
    autokey-gtk -c
    • To start autokey in background, run the command autokey-gtk without any command line arguments:
    autokey-gtk

  2. How can I have autokey run in background and start at login to my linux session?

    • Use systemctl, autokey-gtk commands and i3 directive exec.
    • systemctl: control the systemd system and service manager.
    • exec: executes bash commands in the i3wm config file ~/.config/i3/config.
    • If you want autokey to start in background when you login to your linux session, use the systemd and add it the systemd unit file ~/.config/systemd/user/autokey.service:
    [Unit]
Description=Desktop automation for Linux and X11
Documentation=https://github.com/autokey/autokey

[Service]
Type=notify
ExecStart=/home/tony/.local/bin/autokey-gtk
ExecStop=/bin/systemctl show --property MainPID --value emacs --user | kill
Restart=always

[Install]
WantedBy=default.target
    • Then you have to enable the service and start it. To do so, run the command:
    systemctl --user enable autokey
systemctl --user start autokey

  3. Where are stored autokey config files?

    • autokey config files are in ~/.config/autokey/ directory.

  4. Where can I find autokey ressources?