https://github.com/rodrigobdz/linux-cheatsheet
Collection of useful Linux commands
https://github.com/rodrigobdz/linux-cheatsheet
centos certification-prep command-line debian disk-space docker docker-compose filesystem linux peripherals ubuntu usb-devices
Last synced: 4 months ago
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Collection of useful Linux commands
- Host: GitHub
- URL: https://github.com/rodrigobdz/linux-cheatsheet
- Owner: rodrigobdz
- Created: 2021-01-02T14:44:00.000Z (over 5 years ago)
- Default Branch: main
- Last Pushed: 2022-05-28T14:56:08.000Z (about 4 years ago)
- Last Synced: 2025-10-09T03:42:21.894Z (9 months ago)
- Topics: centos, certification-prep, command-line, debian, disk-space, docker, docker-compose, filesystem, linux, peripherals, ubuntu, usb-devices
- Homepage:
- Size: 69.3 KB
- Stars: 9
- Watchers: 1
- Forks: 1
- Open Issues: 0
-
Metadata Files:
- Readme: readme.md
Awesome Lists containing this project
README
# Linux Cheatsheet
**Highly recommended:** [tldr-pages/tldr](https://github.com/tldr-pages/tldr) ([website](https://tldr.sh))
> collection of community-maintained help pages for command-line tools, that aims to be a simpler, more approachable
> complement to traditional man pages.
---
- [Linux Cheatsheet](#linux-cheatsheet)
- [OS-specific](#os-specific)
- [CentOS](#centos)
- [Ubuntu](#ubuntu)
- [System-wide configuration](#system-wide-configuration)
- [System Services](#system-services)
- [Logs](#logs)
- [Networking](#networking)
- [SSH](#ssh)
- [Env vars](#env-vars)
- [Filesystem](#filesystem)
- [Peripherals](#peripherals)
- [Further Reading](#further-reading)
- [Default editor](#default-editor)
- [Disk Space](#disk-space)
- [RAM](#ram)
- [Swap Memory](#swap-memory)
- [User-specific configuration](#user-specific-configuration)
- [Git](#git)
- [GPG](#gpg)
- [Docker](#docker)
- [Docker in Docker (DinD)](#docker-in-docker-dind)
- [Update a Docker image](#update-a-docker-image)
- [Image Manipulation](#image-manipulation)
- [PDF manipulation](#pdf-manipulation)
- [Optimization](#optimization)
- [Parallel](#parallel)
- [Time](#time)
- [Copy dirs and files](#copy-dirs-and-files)
- [String manipulation](#string-manipulation)
- [Shell Scripting](#shell-scripting)
- [Related Projects](#related-projects)
## OS-specific
### CentOS
- [Yum Command Cheat
Sheet](https://access.redhat.com/sites/default/files/attachments/rh_yum_cheatsheet_1214_jcs_print-1.pdf)
### Ubuntu
- Unattended reboot
```sh
sudo editor /etc/gdm3/custom.conf
# Uncomment the following lines and change user1 to the value of $USER:
# AutomaticLoginEnable = true
# AutomaticLogin = user1
```
- [Debian Unattended Upgrades](https://wiki.debian.org/UnattendedUpgrades)
- Reinstall Unity on Ubuntu
```sh
sudo apt-get update
sudo apt-get install --reinstall ubuntu-desktop
sudo apt-get install --reinstall unity
```
- Fix `mesg: ttyname failed: Inappropriate ioctl for device`
Comment out `mesg n || true` in `/root/.profile`:
```sh
# mesg n || true
test -t 0 && mesg n
```
[Source](https://superuser.com/a/1277604)
## System-wide configuration
### System Services
- Print service definition
```sh
systemctl cat SERVICE_NAME.service
```
### Logs
- Recover logs from failed `/etc/fstab` during boot
- Search by **date**
```sh
journalctl --since today
```
- Search by **keyword**
```sh
grep --ignore-case --regexp=KEYWORD --files-with-matches --dereference-recursive /var/log 2> /dev/null
```
- Search by **file**
```sh
journalctl --file /var/log/FILENAME.journal
```
### Networking
- Connect to network on interface `eth0` on boot
```sh
sudo systemctl status network
sudo editor /etc/sysconfig/network-scripts/ifcfg-eth0
# Set ONBOOT=yes for desired network
```
- Set DNS server
```sh
editor /etc/resolv.conf
# Add DNS server
# Example:
# nameserver 8.8.8.8
```
[Source](https://developers.google.com/speed/public-dns/docs/using)
- List kernel routing tables
```sh
route --numeric
```
#### SSH
- Generate SSH key
```sh
# -t specifies the type of key to generate
# -C provides a comment for the key
ssh-keygen -t ed25519 -C "your_email@example.com"
```
[Source](https://docs.github.com/en/authentication/connecting-to-github-with-ssh/generating-a-new-ssh-key-and-adding-it-to-the-ssh-agent)
- Test passphrase for SSH key
```sh
# -y "This option will read a private OpenSSH format file and print an OpenSSH public key to stdout."
ssh-keygen -y -f
```
- Regenerate remote host identification entry in `known_hosts` file
```sh
ssh-keygen -f "~/.ssh/known_hosts" -R
```
- [SSH Message Numbers](https://www.iana.org/assignments/ssh-parameters/ssh-parameters.xhtml#ssh-parameters-1)
Examples:
> send packet: type 50 receive packet: type 51
### Env vars
- Given a file named `example.env` with contents:
```sh
a='jane'
b='john'
c='doe'
```
- Source all variables:
```sh
source example.env
```
- Export all variables in file
```sh
# After sourcing all variables, we can export them
export $(cut --delimiter= --fields=1 example.env)
```
[Source](https://unix.stackexchange.com/a/79065)
### Filesystem
- Filesystem Hierarchy Standard (FHS)
> The Filesystem Hierarchy Standard (FHS) defines the directory structure and directory contents in Linux
> distributions. [Source](https://en.m.wikipedia.org/wiki/Filesystem_Hierarchy_Standard)
---
- List 5 largest files in folder and sort by size
```sh
du --human-readable --summarize * | sort --reverse --human-numeric-sort | head --lines 5
```
- Report file system disk space usage
```sh
df --human-readable
```
- Create filesystem on external disk
```sh
# Create filesystem
mkfs.ext4 /dev/vdb
# Create mountpoint directory
mkdir --parents /data
# Mount external disk to /data
mount /dev/vdb /data
```
- Mount from `/etc/fstab`
```sh
mount --all
```
- List all partitions and their Universally Unique Identifier (UUID)
```sh
sudo blkid
```
- Create sequence of numbered directories
```sh
# Creates directories 1/ ... 10/
mkdir -p $(seq 1 10)
```
### Peripherals
- Cheatsheet from `opensource.com`: [Linux commands to display your hardware
information](https://opensource.com/article/19/9/linux-commands-hardware-information)
As a general rule device shown in `/dev/sd*` are storage devices as opposed to the ones shown in `/dev/bus`.
- List connected system devices
```sh
find /dev/sd*
```
- List available USB ports
- Simple
```sh
find /dev/bus/
```
- Advanced
```sh
ls /sys/bus/usb/devices/*
```
- Display info for specific USB device
```sh
sudo lsusb -D /dev/bus/usb/001/005
```
- List block devices
```sh
lsblk
```
- List the partition tables for the specified devices
```sh
sudo fdisk --list
```
- List hardware
```sh
sudo lshw
```
- List hardware (only input devices)
```sh
sudo lshw -class disk -class input -short
```
- List USB devices
- `usb-devices`
> usb-devices is a (bash) shell script that can be used to display details of USB buses in the system and the
> devices connected to them.
```sh
usb-devices
```
[Source](https://linux.die.net/man/1/usb-devices)
- `lsusb`
> lsusb is a utility for displaying information about USB buses in the system and the devices connected to them
```sh
lsusb
```
[Source](https://linux.die.net/man/1/usb-devices)
- `usbview`
> usbview provides a **graphical** summary of USB devices connected to the system. Detailed information may be
> displayed by selecting individual devices in the tree display.
```sh
usbview
```
[Source](https://linux.die.net/man/1/usb-devices)
#### Further Reading
- [Interpreting the output of lsusb](https://diego.assencio.com/?index=1363692dafeabeff8e3f975077f92dfe)
- [Find USB device details in Linux/Unix using LSUSB
command](https://www.linuxnix.com/find-usb-device-details-in-linuxunix-using-lsusb-command/)
- [USB Descriptors](https://www.beyondlogic.org/usbnutshell/usb5.shtml)
### Default editor
- Set default editor for `sudo systemctl edit --full SERVICE_NAME`
```sh
sudo update-alternatives --config editor
```
### Disk Space
- Check available disk space
```sh
df --human-readable / | awk 'END{print $4}' | cut --delimiter='G' --fields=1
```
### RAM
- Check available RAM
```sh
free --total --gibi | awk '/Total:/ { print $2 }'
```
### Swap Memory
- Configure swap memory (run as `root` user)
```sh
configure_swap_memory() {
local -r swap_file_path="$1"
local -r swap_memory_size_in_gb="$2"
set -o errexit
set -o pipefail
set -o nounset
echo 'Disable all swap memory temporarily'
swapoff --all
# ATTENTION: fallocate is faster than dd but some systems require dd usage.
# If the fallocate command below fails, use the following instead:
#
# size=$((swap_memory_size_in_gb * 1024))
# sudo dd if=/dev/zero of="$swap_file_path" count=$size bs=1MiB
#
echo "Create $swap_file_path of size ${swap_memory_size_in_gb}GB"
fallocate --length "${swap_memory_size_in_gb}G" "$swap_file_path"
echo "Set up a Linux swap area in file $swap_file_path"
mkswap "$swap_file_path"
echo "Enable file $swap_file_path for paging and swapping"
swapon "$swap_file_path"
echo "Setting file permissions to 0600 of $swap_file_path"
chmod 600 "$swap_file_path"
echo 'Verify increased size of swap memory'
grep SwapTotal /proc/meminfo
}
configure_swap_memory '/swapfile' 8
```
- [Recommended size of swap space](https://opensource.com/article/18/9/swap-space-linux-systems)
## User-specific configuration
- Set locale
Follow the instructions below to fix the following warnings:
> perl: warning: Setting locale failed.
>
> perl: warning: Please check that your locale settings:
>
> LANGUAGE = (unset),
>
> LC_ALL = (unset),
>
> LC_CTYPE = "UTF-8",
>
> LANG = "en_US.UTF-8"
>
> are supported and installed on your system.
>
> perl: warning: Falling back to the standard locale ("C").
Append the following lines to `~/.bashrc`:
```sh
export LANGUAGE=en_US.UTF-8
export LC_ALL=en_US.UTF-8
export LANG=en_US.UTF-8
export LC_CTYPE=en_US.UTF-8
```
- Preserve env when executing `sudo`
```sh
sudo --preserve-env
```
- Print non-root username
```sh
# Returns name of user with UID 1000 (defaults to non-root user)
uid=1000
getent passwd "$uid" | cut -d: -f1
```
[Source](https://unix.stackexchange.com/a/36582)
Alternatively:
```sh
# "SUDO_USER Set to the login name of the user who invoked sudo."
echo $SUDO_USER
```
[Source](https://man7.org/linux/man-pages/man8/sudo.8.html)
## Git
- Mark all subdirectories as safe in git
```sh
# ls options
# -1 list one file per line
#
# xargs options
# -L max. lines
\ls -1 --directory $PWD/. | xargs -L 1 --delimiter='\n' git config --global --add safe.directory
```
- Delete local and remote tag
```sh
# Delete local tag
git tag --delete
# Delete remote tag
git push --delete origin
```
- Rename local and remote branch
```sh
# Placeholders: old_name new_name
# If old_name not checked out already
git checkout old_name
# Rename local branch
git branch -m old_name new_name
# Delete old_name remote branch and push new_name local branch
git push origin :old_name new_name
# Reset upstream branch fo new_name local branch
git push origin --set-upstream new_name
```
[Source](https://stackoverflow.com/questions/30590083/how-do-i-rename-both-a-git-local-and-remote-branch-name/45561865#45561865)
- List changed files on branch with regard to main branch
```sh
git --no-pager diff --name-only FETCH_HEAD $(git merge-base FETCH_HEAD main)
```
[Source](https://stackoverflow.com/questions/25071579/list-all-files-changed-in-a-pull-request-in-git-github/25071749#25071749)
- Improve performance of `git clone`
Read GitHub's [performance
comparison](https://github.blog/2020-12-22-git-clone-a-data-driven-study-on-cloning-behaviors/) for `git clone` and
[introduction to shallow and partial
clone](https://github.blog/2020-12-21-get-up-to-speed-with-partial-clone-and-shallow-clone/#:~:text=git%20clone%20%2D%2Dfilter%3Dtree,need%20access%20to%20commit%20history.)
- Solve merge conflict
```sh
git mergetool
```
- Check performance metrics and recommendations for git repo using [git-sizer](https://github.com/github/git-sizer)
```sh
git-sizer --verbose
```
- List biggest files in `.git` folder
```sh
git rev-list --objects --all \
| git cat-file --batch-check='%(objecttype) %(objectname) %(objectsize) %(rest)' \
| sed --quiet 's/^blob //p' \
| sort --numeric-sort --key=2 \
| tail --lines 10 \
| cut --characters=1-12,41- \
| $(command -v gnumfmt || echo numfmt) --field=2 --to=iec-i --suffix=B --padding=7 --round=nearest
```
[Source](https://stackoverflow.com/questions/9456550/how-to-find-the-n-largest-files-in-a-git-repository/46085465#46085465)
- Git pull all repos in a directory
```sh
find . -type d -depth 1 -exec git --git-dir={}/.git --work-tree=$PWD/{} pull \;
```
[Source](https://stackoverflow.com/a/12495234/2227405)
## GPG
- List all keys in long-format
```sh
gpg --list-secret-keys --keyid-format LONG
```
- Generate a new GPG key pair
```sh
gpg --full-generate-key
# Follow instructions from link below
```
[Source](https://docs.github.com/en/github/authenticating-to-github/generating-a-new-gpg-key)
- Delete GPG key pair
```sh
# Delete secret key
gpg --delete-secret-key
# Delete public key
gpg --delete-key
```
- Renew expired yarn GPG key
```sh
curl -sS https://dl.yarnpkg.com/debian/pubkey.gpg | sudo apt-key add -
```
[Source](https://github.com/yarnpkg/yarn/issues/7866#issue-558663837)
## Docker
- Watch status of Docker containers
You may need to install the `watch` command depending on your Linux distribution.
```sh
# Interval unit is seconds
watch --interval 1 'docker ps -a'
```
- Enter a crashing Docker container
```sh
docker commit my-broken-container
docker run --interactive --tty my-broken-container /bin/bash
```
- Check cause of container crash
```sh
dmesg --ctime | grep --extended-regexp --ignore-case --before-context=100 'killed process'
```
- Find absolute path to Docker volume in file system
```sh
docker volume inspect --format '{{ .Mountpoint }}' VOLUME_NAME
```
- Search local Docker images by name
```sh
# Replace placeholder IMAGENAME by Docker image name you are searching for
docker images '*IMAGENAME*'
```
### Docker in Docker (DinD)
The trick is to mount `/var/run/docker.sock` as a volume. The Docker container can then access Docker on the host.
[Source](https://itnext.io/docker-in-docker-521958d34efd)
### Update a Docker image
The following image uses the image `my_image:my_tag` as a placeholder.
```sh
# Replace placeholder image_name with the name of the image you want to update
image_name=my_image:my_tag
container_name=update-image-container
# Start a container with the image to update
docker run --rm --tty --detach --name "$container_name" "$image_name"
# Log into the image to update it
docker exec --interactive --tty "$container_name" bash
# Update the image (the following command is executed inside the image). Example:
touch /tmp/new_file.txt
# Exit the image
exit
# Commit the image, i.e., create a new image from the container’s changes
docker commit "$container_name" "$image_name"
docker stop "$container_name"
```
## Image Manipulation
[Source](https://tldr.ostera.io/convert)
- Horizontally append images
```sh
convert *.png +append horizontal-image.png
```
- Vertically append images
```sh
convert *.png -append vertical-image.png
```
- Create image with white background
```sh
convert -size 32x32 xc:white empty.jpg
```
- Replace alpha channel with white background in all PNG images in nested directories
```sh
for i in `ls -1 **/*.png`; do convert $i -background white -alpha remove -alpha off $i; done
```
[Source](https://stackoverflow.com/a/52962485)
- Export multiple PNG images to PDF using [img2pdf](https://gitlab.mister-muffin.de/josch/img2pdf)
```sh
# Enter directory containing PNGs
cd directory-with-images/
# Remove alpha from images and convert colorspace to RGB (img2pdf does not support ICC)
for i in *.png; convert $i -colorspace rgb -alpha off $i; end
# Merge images into PDF
# (Optional) Add --pagesize A4 to normalize page size
img2pdf --output merged.pdf *.png
# (Optional) To add OCR text layer, execute the following line
# ocrmypdf --force-ocr merged.pdf merged.pdf
```
## PDF manipulation
- Add OCR text layer to PDF using [ocrmypdf](https://github.com/jbarlow83/OCRmyPDF)
```sh
ocrmypdf --force-ocr input.pdf output.pdf
```
- Merge PDFs
```sh
pdfunite in-1.pdf in-2.pdf out.pdf
```
- Reduce PDF file size
Requires [`gs`](https://www.ghostscript.com/) and [`shrinkpdf`](http://www.alfredklomp.com/programming/shrinkpdf/) installation
```sh
shrinkpdf in.pdf out.pdf
```
- Search for text in PDF using [pdfgrep](https://pdfgrep.org/)
```sh
pdfgrep pattern file.pdf
```
## Optimization
### Parallel
- Run command in parallel using GNU parallel
```sh
parallel --halt-on-error now,fail=1 'set -o errexit; set -o pipefail; set -o nounset; echo {}' ::: 1 2 3
```
[Parallel manual](https://www.gnu.org/software/parallel/parallel_tutorial.html)
### Time
- Schedule command execution at specific time and date
```sh
at hh:mm
```
- Store output of time command in variable without output of argument
```sh
# Format output of time command
# Source: https://www.gnu.org/savannah-checkouts/gnu/bash/manual/bash.html#index-TIMEFORMAT
TIMEFORMAT='Elapsed time in seconds: %lR'
# Quoting from http://mywiki.wooledge.org/BashFAQ/032:
# Keep stdout untouched.
# The shell's original file descriptor (FD) 1 is saved in FD 3, which is inherited by the subshell.
# Inside the innermost block, we send the time command's stdout to FD 3.
exec 3>&1
# Captures stderr and time.
elapsed_time=$( { time ls 1>&3; } 2>&1 )
exec 3>&-
echo "$elapsed_time"
```
[Source](http://mywiki.wooledge.org/BashFAQ/032)
### Copy dirs and files
- Base `rsync` options
```sh
rsync --archive --compress --verbose --human-readable --progress [PATH] [PATH]
```
- Display overall progress in rsync
```sh
# Use rsync options --info=progress2 and --no-inc-recursive
# Example:
cd /tmp/bar && find . -type -f | parallel --halt-on-error now,fail=1 -X rsync --relative--no-inc-recursive --info=progress2 --human-readable './{}' /tmp/bar/ ; }
```
- Transfer large files efficiently
```sh
# Options
# WARNING: Add --compress to RSYNC_OPTS only if transferring over a slow connection.
# For local transfers --compress actually slows down the operation
readonly RSYNC_OPTS=(--hard-links --archive --relative --partial '--info=progress2' --human-readable)
readonly RSYNC_EXCLUDES=(--exclude=archive
--exclude=.git
--exclude=.gitignore
--exclude=.idea
--exclude=.vagrant
--exclude=__pycache__
--exclude=*.swp
--exclude=.vscode)
# 0 jobs in parallel translates to as many as possible
readonly NUMBER_OF_JOBS=0
cd src-dir && find . -type f | parallel --jobs "$NUMBER_OF_JOBS" --halt-on-error now,fail=1 -X rsync "${RSYNC_OPTS[@]}" "${RSYNC_EXCLUDES[@]}" ./{} dest-dir/
```
[Source](https://www.gnu.org/software/parallel/man.html#EXAMPLE:-Parallelizing-rsync)
## String manipulation
- Replace characters in filenames found in current working directory
```sh
# Replace all occurrences of underscores in filenames of files in current working directory with a hyphen
for f in *; do mv $f ${f//_/-}; done
```
## Shell Scripting
- Script template:
- Robust and [portable](https://www.cyberciti.biz/tips/finding-bash-perl-python-portably-using-env.html) shebang
- Recommended bash/shell options for scripts
- Inherit shell options in subshells
[Example](https://stackoverflow.com/a/20832592/2227405) [`SHELLOPTS`
docs](https://www.gnu.org/software/bash/manual/html_node/Bash-Variables.html)
```sh
#!/usr/bin/env bash
#
# Script description
# Bash options
# Inherit errexit in subshells (requires Bash 4.4+)
shopt -s inherit_errexit
# Shell options
set -o errexit
set -o pipefail
set -o nounset
# Export enabled shell options to subshells
# Documentation:
# https://www.gnu.org/software/bash/manual/html_node/Bash-Variables.html
export SHELLOPTS
```
- [Bash FAQ](http://mywiki.wooledge.org/BashFAQ)
- [Bash Study Guide](https://fvue.nl/wiki/Bash)
- [Bash variables](https://www.gnu.org/software/bash/manual/html_node/Bash-Variables.html)
- Conditionally pass arguments to command
```sh
declare conditional_rename=()
if [ true ]; then
# Including value of variable in case it's not empty
conditional_rename=("${conditional_rename[@]}" --before-context=3)
fi
# Converts to grep --before-context=3 'sh' readme.md
grep "${conditional_rename[@]}" 'sh' readme.md
```
## Related Projects
- [macos-cheatsheet](https://github.com/rodrigobdz/macos-cheatsheet)
- [modern-unix](https://github.com/ibraheemdev/modern-unix)