889 commands · 48 cheat sheets · 6 subcategories

Linux master quick reference

Browse 223 commands from 12 focused cheat sheets on page 1 of 4. Each example opens its matching detailed section.

Shell, Files, and Automation · 20 commands

Bash Scripting Cheat Sheet

Use	Syntax	Examples
Select Bash through PATH	`#!/usr/bin/env bash`	View examples
Enable stricter failure handling	`set -Eeuo pipefail`	View examples
Read an argument	`input=${1:?usage: script INPUT}`	View examples
Supply a default	`mode=${MODE:-safe}`	View examples
Preserve one argument	`printf '%s\n' "$filename"`	View examples
Create an array	`files=("report one.txt" "report two.txt")`	View examples
Pass every array member	`command -- "${files[@]}"`	View examples
Read a literal line	`IFS= read -r line`	View examples
Process a file line by line	`while IFS= read -r line; do printf '%s\n' "$line"; done \ < input.txt`	View examples
Test a regular file	`if [[ -f $path ]]; then process "$path"; fi`	View examples
Compare integers	`if (( count > 10 )); then printf 'large\n'; fi`	View examples
Match alternatives	`case $mode in safe\|fast) run "$mode" ;; *) exit 2 ;; \ esac`	View examples
Define a function	`log() { printf '%s\n' "$*" >&2; }`	View examples
Keep function state local	`local path=$1`	View examples
Parse short options	`while getopts ':o:v' option; do case $option in o) \ output=$OPTARG ;; v) verbose=1 ;; esac; done`	View examples
Remove parsed options	`shift "$((OPTIND - 1))"`	View examples
Create a temporary directory	`workdir=$(mktemp -d)`	View examples
Clean up on exit	`trap 'rm -rf -- "$workdir"' EXIT`	View examples
Check syntax	`bash -n script.sh`	View examples
Run static analysis	`shellcheck script.sh`	View examples

Shell, Files, and Automation · 18 commands

Cron, at, and Anacron Scheduling Cheat Sheet

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Use	Syntax	Examples
List personal crontab	`crontab -l`	View examples
Edit personal crontab	`crontab -e`	View examples
Validate a Cronie table	`crontab -T ./app.crontab`	View examples
Install a reviewed table	`crontab ./app.crontab`	View examples
Run on weekday mornings	`15 6 * * 1-5 /usr/local/bin/report-job`	View examples
Run every 15 minutes	`/15 * * * /usr/local/bin/health-sample`	View examples
Select Cronie timezone	`CRON_TZ=UTC`	View examples
Set a deterministic PATH	`PATH=/usr/local/bin:/usr/bin:/bin`	View examples
Define a system cron job	`20 2 * * * backup /usr/local/libexec/app-backup`	View examples
Prevent overlapping runs	`flock -n /run/user/1000/report.lock \ /usr/local/bin/report-job`	View examples
Queue commands from a file	`at -f ./maintenance.sh 02:30 tomorrow`	View examples
List queued at jobs	`atq`	View examples
Inspect an at job	`at -c 42`	View examples
Remove an at job	`atrm 42`	View examples
Queue for low load	`batch -f ./index-rebuild.sh`	View examples
Define a weekly catch-up job	`7 20 app-weekly /usr/local/libexec/app-weekly`	View examples
Validate anacrontab	`sudo anacron -T -t /etc/anacrontab`	View examples
Run one due job in foreground	`sudo anacron -d -s app-weekly`	View examples

Shell, Files, and Automation · 20 commands

Linux Archives and Compression Cheat Sheet

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Use	Syntax	Examples
Create a tar archive	`tar -cf project.tar project/`	View examples
Archive relative names	`tar -C /srv/app -cf app.tar config public`	View examples
Exclude generated files	`tar --exclude='*.log' --exclude='cache/' -cf app.tar \ app/`	View examples
List archive members	`tar -tf project.tar`	View examples
Inspect stored metadata	`tar -tvf project.tar`	View examples
Extract an archive	`tar -xf project.tar -C destination/`	View examples
Extract one member	`tar -xf project.tar project/README.md`	View examples
Remove a leading directory	`tar -xf release.tar -C destination/ --strip-components=1`	View examples
Ignore stored ownership	`tar -xf backup.tar -C destination/ --no-same-owner`	View examples
Create a gzip tarball	`tar -czf project.tar.gz project/`	View examples
Create an xz tarball	`tar -cJf project.tar.xz project/`	View examples
Select compression by suffix	`tar -caf project.tar.gz project/`	View examples
Extract compressed tar	`tar -xf project.tar.gz -C destination/`	View examples
Compress and keep a file	`gzip -k report.csv`	View examples
Decompress to standard output	`gzip -dc report.csv.gz \| head`	View examples
Compress with xz	`xz -k report.csv`	View examples
Test gzip integrity	`gzip -t project.tar.gz`	View examples
Test xz integrity	`xz -t project.tar.xz`	View examples
Verify a checksum file	`sha256sum --check project.tar.gz.sha256`	View examples
Review before extraction	`file release.tar.gz && gzip -t release.tar.gz && tar -tf \ release.tar.gz`	View examples

Shell, Files, and Automation · 14 commands

Linux Environment Variables and Shell Startup Cheat Sheet

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Use	Syntax	Examples
Print exported values	`printenv`	View examples
Read one variable	`printenv PATH`	View examples
Set a shell variable	`mode=development`	View examples
Export to children	`export MODE=development`	View examples
Scope to one command	`MODE=development ./app`	View examples
Remove a variable	`unset MODE`	View examples
Prepend a PATH directory	`export PATH="$HOME/.local/bin:$PATH"`	View examples
Resolve a command	`command -v python3`	View examples
Start clean	`env -i PATH=/usr/bin:/bin HOME="$HOME" command`	View examples
Inspect locale	`locale`	View examples
List locales	`locale -a`	View examples
Inspect manager environment	`systemctl show-environment`	View examples
Set a unit variable	`Environment=APP_MODE=production`	View examples
Load an environment file	`EnvironmentFile=/etc/myapp/environment`	View examples

Shell, Files, and Automation · 22 commands

Linux Files and Directories Cheat Sheet

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Use	Syntax	Examples
Show the current directory	`pwd`	View examples
List directory contents	`ls -lah`	View examples
Change directory	`cd /var/log`	View examples
Move to the parent	`cd ..`	View examples
Return home	`cd ~`	View examples
Create nested directories	`mkdir -p project/src/components`	View examples
Create an empty file	`touch notes.txt`	View examples
Identify a file type	`file archive.tar.gz`	View examples
Print a text file	`cat notes.txt`	View examples
Read the first lines	`head -n 20 app.log`	View examples
Read the last lines	`tail -n 20 app.log`	View examples
Follow a growing log	`tail -f app.log`	View examples
Copy a file safely	`cp -i config.ini config.ini.bak`	View examples
Copy a directory tree	`cp -a project project-backup`	View examples
Move or rename an item	`mv -i draft.txt final.txt`	View examples
Find files by name	`find . -type f -name '*.json'`	View examples
Find recently changed files	`find . -type f -mtime -7`	View examples
Search text recursively	`grep -RIn --exclude-dir=.git 'TODO' .`	View examples
Measure directory size	`du -sh project`	View examples
Remove a file interactively	`rm -i obsolete.txt`	View examples
Remove an empty directory	`rmdir empty-directory`	View examples
Remove a directory tree	`rm -rI build-output`	View examples

Shell, Files, and Automation · 20 commands

Linux Text Processing Cheat Sheet

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Use	Syntax	Examples
Find matching lines	`grep 'ERROR' app.log`	View examples
Match literal text	`grep -F 'user[id]' app.log`	View examples
Ignore letter case	`grep -i 'warning' app.log`	View examples
Show line numbers	`grep -n 'timeout' app.log`	View examples
Exclude matching lines	`grep -v '^#' settings.conf`	View examples
Use extended patterns	`grep -E 'ERROR\|WARN' app.log`	View examples
Replace the first match	`sed 's/http:/https:/' links.txt`	View examples
Replace every match	`sed 's/[[:space:]]\{1,\}/ /g' notes.txt`	View examples
Remove matching lines	`sed '/^[[:space:]]*$/d' notes.txt`	View examples
Print selected fields	`awk -F',' '{print $1, $3}' records.csv`	View examples
Filter numeric fields	`awk -F',' '$3 >= 80 {print $1, $3}' scores.csv`	View examples
Sum a column	`awk -F',' 'NR > 1 {sum += $3} END {print sum}' sales.csv`	View examples
Extract delimited fields	`cut -d: -f1,7 /etc/passwd`	View examples
Sort text	`sort names.txt`	View examples
Sort numerically	`sort -t, -k2,2n scores.csv`	View examples
Count repeated lines	`sort statuses.txt \| uniq -c`	View examples
Convert letter case	`tr '[:lower:]' '[:upper:]' < names.txt`	View examples
Delete characters	`tr -d '\r' < windows.txt`	View examples
Count lines	`wc -l < app.log`	View examples
Summarize a field	`awk -F',' 'NR > 1 {print $2}' requests.csv \| sort \| uniq -c \| sort -nr`	View examples

Shell, Files, and Automation · 17 commands

rsync and Incremental Backups Cheat Sheet

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Use	Syntax	Examples
Copy directory contents	`rsync -a /srv/app/ /backup/app/`	View examples
Copy directory by name	`rsync -a /srv/app /backup/`	View examples
Preserve ACLs and xattrs	`sudo rsync -aAX /srv/app/ /backup/app/`	View examples
Stay on one filesystem	`rsync -a --one-file-system /srv/ /backup/srv/`	View examples
Preview itemized changes	`rsync -ain /srv/app/ /backup/app/`	View examples
Read exclude patterns	`rsync -a --exclude-from=/etc/backup/app.exclude \ /srv/app/ /backup/app/`	View examples
Mirror with delayed deletion	`rsync -ain --delete-delay --max-delete=100 /srv/app/ \ /backup/app/`	View examples
Retain replaced destination files	`rsync -a --backup --backup-dir=../changed /srv/app/ \ /backup/current/`	View examples
Push through SSH	`rsync -a -e 'ssh -o BatchMode=yes' /srv/app/ \ backup@store.example:/vault/app/`	View examples
Protect remote arguments	`rsync -a -s ./data/ \ backup@store.example:'/vault/team data/'`	View examples
Bound idle network time	`rsync -a --timeout=120 --partial-dir=.rsync-partial \ /srv/app/ backup@store.example:/vault/app/`	View examples
Build a hard-linked snapshot	`rsync -a --link-dest=../previous /srv/app/ \ /backup/snapshots/2026-08-12/`	View examples
Audit snapshot changes	`rsync -ain --link-dest=../previous /srv/app/ \ /backup/snapshots/next/`	View examples
Checksum-compare a restore	`rsync -nric --delete /backup/restore-test/ \ /srv/restore-reference/`	View examples
Preview a restore	`rsync -ain /backup/snapshots/2026-08-12/ \ /srv/restore-test/`	View examples
Inspect local rsync version	`rsync --version`	View examples
Print transfer statistics	`rsync -a --stats /srv/app/ /backup/app/`	View examples

Identity, Access, and Security · 20 commands

AppArmor Profiles and Troubleshooting Cheat Sheet

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Use	Syntax	Examples
Check module availability	`aa-enabled`	View examples
Inspect loaded policy	`sudo aa-status`	View examples
Inspect one task label	`pid=$(systemctl show reportd.service -p MainPID \ --value); sudo cat "/proc/$pid/attr/current"`	View examples
Find recent denials	`sudo journalctl -k --grep='apparmor="DENIED"' \ --since='15 minutes ago'`	View examples
Query Audit records	`sudo ausearch -m AVC,USER_AVC -ts recent \| grep 'apparmor="DENIED"'`	View examples
Include base abstraction	`#include <abstractions/base>`	View examples
Include local overrides	`#include if exists <local/usr.local.bin.reportd>`	View examples
Allow recursive reads	`/srv/reporting/** r,`	View examples
Allow directory traversal	`/srv/reporting/ r,`	View examples
Limit writes to owned files	`owner /var/lib/reportd/** rwk,`	View examples
Execute without transition	`/usr/bin/logger ix,`	View examples
Allow TCP networking	`network inet stream,`	View examples
Validate without loading	`apparmor_parser -Q /etc/apparmor.d/usr.local.bin.reportd`	View examples
Expand includes	`apparmor_parser -p /etc/apparmor.d/usr.local.bin.reportd`	View examples
Replace one loaded profile	`sudo apparmor_parser -r \ /etc/apparmor.d/usr.local.bin.reportd`	View examples
Load complain mode temporarily	`sudo apparmor_parser -C -r \ /etc/apparmor.d/usr.local.bin.reportd`	View examples
Persist complain mode	`sudo aa-complain /usr/local/bin/reportd`	View examples
Restore enforce mode	`sudo aa-enforce /usr/local/bin/reportd`	View examples
Review logged behavior	`sudo aa-logprof`	View examples
Disable one profile	`sudo aa-disable /usr/local/bin/reportd`	View examples

Identity, Access, and Security · 14 commands

Linux Audit Framework and auditd Cheat Sheet

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Use	Syntax	Examples
Inspect kernel audit status	`sudo auditctl -s -i`	View examples
Inspect the audit daemon	`sudo systemctl status auditd --no-pager`	View examples
List active kernel rules	`sudo auditctl -l`	View examples
Check whether rules changed	`sudo augenrules --check`	View examples
Build the merged rules file	`sudo augenrules`	View examples
Build and load persistent rules	`sudo augenrules --load`	View examples
Audit writes and metadata changes	`-a always,exit -F arch=b64 -F path=/etc/sudoers -F \ perm=wa -k sudoers_change`	View examples
Audit a directory tree	`-a always,exit -F arch=b64 -F dir=/etc/sudoers.d/ -F \ perm=wa -k sudoers_change`	View examples
Audit failed file access	`-a always,exit -F arch=b64 -S openat,truncate -F \ dir=/etc/ -F success=0 -k etc_access_denied`	View examples
Search by rule key	`sudo ausearch --start today --key sudoers_change -i`	View examples
Search failed events	`sudo ausearch --start recent --success no -i`	View examples
Summarize authentication activity	`sudo aureport --auth --summary -i`	View examples
Request auditd internal state	`sudo auditctl --signal state`	View examples
Lock the audit configuration	`-e 2`	View examples

Identity, Access, and Security · 20 commands

Linux Capabilities and File Attributes Cheat Sheet

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Use	Syntax	Examples
Read process capability masks	`grep -E '^Cap(Inh\|Prm\|Eff\|Bnd\|Amb):' /proc/1234/status`	View examples
Decode a capability mask	`capsh --decode=0000000000000400`	View examples
Show current capability context	`capsh --print`	View examples
Read file capabilities	`getcap -v /usr/local/bin/ping-helper`	View examples
Scan one filesystem tree	`sudo getcap -r /usr/local 2>/dev/null`	View examples
Grant network bind capability	`sudo setcap 'cap_net_bind_service=ep' \ /usr/local/bin/webd`	View examples
Remove file capabilities	`sudo setcap -r /usr/local/bin/webd`	View examples
Verify expected capability	`getcap /usr/local/bin/webd \| grep -F 'cap_net_bind_service=ep'`	View examples
Show highest supported capability	`cat /proc/sys/kernel/cap_last_cap`	View examples
Check no-new-privileges	`grep '^NoNewPrivs:' /proc/1234/status`	View examples
Inspect unit capability policy	`systemctl show webd.service -p CapabilityBoundingSet -p \ AmbientCapabilities -p NoNewPrivileges`	View examples
Analyze unit exposure	`systemd-analyze security webd.service`	View examples
List file attributes	`lsattr -d /etc/important.conf`	View examples
Set immutable	`sudo chattr +i /etc/important.conf`	View examples
Clear immutable	`sudo chattr -i /etc/important.conf`	View examples
Set append-only	`sudo chattr +a /var/log/example.log`	View examples
List extended attributes	`getfattr --dump --absolute-names /usr/local/bin/webd`	View examples
Read raw capability xattr	`getfattr --name=security.capability --hex \ /usr/local/bin/webd`	View examples
Copy while preserving xattrs	`cp --archive --preserve=xattr /usr/local/bin/webd \ /srv/stage/webd`	View examples
Archive with xattrs	`tar --xattrs --acls -cpf webd-backup.tar \ /usr/local/bin/webd`	View examples

Identity, Access, and Security · 20 commands

Linux PAM Authentication Cheat Sheet

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Use	Syntax	Examples
List PAM service files	`find /etc/pam.d -maxdepth 1 -type f -print \| sort`	View examples
Read PAM overview	`man 8 pam`	View examples
Read configuration syntax	`man 5 pam.d`	View examples
Find auth rules	`grep -RnsE '^[[:space:]]*auth[[:space:]]' /etc/pam.d`	View examples
Find account rules	`grep -RnsE '^[[:space:]]*account[[:space:]]' /etc/pam.d`	View examples
Find password rules	`grep -RnsE '^[[:space:]]*password[[:space:]]' /etc/pam.d`	View examples
Find session rules	`grep -RnsE '^[[:space:]]*session[[:space:]]' /etc/pam.d`	View examples
Find included stacks	`grep -RnsE \ '^[[:space:]]*(auth\|account\|password\|session)[[:space:]]+(include\|substack)' \ /etc/pam.d`	View examples
List PAM modules	`find /usr/lib /lib -type f -name 'pam_*.so' -print \ 2>/dev/null \| sort -u`	View examples
Show lock records	`sudo faillock --user alice`	View examples
Reset one lockout	`sudo faillock --user alice --reset`	View examples
Read lockout policy	`grep -Ev '^[[:space:]]*(#\|$)' \ /etc/security/faillock.conf`	View examples
Read access rules	`grep -Ev '^[[:space:]]*(#\|$)' /etc/security/access.conf`	View examples
Read resource limits	`grep -RhvE '^[[:space:]]*(#\|$)' \ /etc/security/limits.conf /etc/security/limits.d`	View examples
Read password quality policy	`grep -RhvE '^[[:space:]]*(#\|$)' \ /etc/security/pwquality.conf \ /etc/security/pwquality.conf.d`	View examples
Test one PAM service	`sudo pamtester login alice authenticate`	View examples
Test account management	`sudo pamtester login alice acct_mgmt`	View examples
Check SSH PAM integration	`sshd -T \| grep -i '^usepam'`	View examples
Read authentication logs	`journalctl _COMM=sudo --since '-15 minutes' --no-pager`	View examples
Identify module package	`rpm -qf /usr/lib64/security/pam_unix.so`	View examples

Identity, Access, and Security · 18 commands

Linux Permissions Cheat Sheet

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Use	Syntax	Examples
List permission strings	`ls -l`	View examples
Show a numeric mode	`stat -c '%A %a %U %G %n' file`	View examples
Show current identity	`id`	View examples
Add owner execute	`chmod u+x script.sh`	View examples
Remove group and other write	`chmod go-w file`	View examples
Assign exact symbolic modes	`chmod u=rw,g=r,o= file`	View examples
Set a private file mode	`chmod 640 secrets.env`	View examples
Set a directory mode	`chmod 750 scripts`	View examples
Apply a recursive mode	`chmod -R --preserve-root u=rwX,g=rX,o= project`	View examples
Change a file owner	`sudo chown alice file`	View examples
Change owner and group	`sudo chown alice:developers path`	View examples
Change the owning group	`sudo chgrp developers path`	View examples
Show the current umask	`umask`	View examples
Set a restrictive umask	`umask 027`	View examples
Inherit a directory group	`chmod g+s shared`	View examples
Protect shared entries	`chmod +t shared`	View examples
Find world-writable files	`find . -type f -perm -o=w -print`	View examples
Find executable files	`find . -type f -perm /111 -print`	View examples

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