bash
getent passwd aliceNotes
Useful on systems backed by LDAP or other NSS sources.
Linux Permissions and Security Cheat Sheet
High-value Linux permissions and security reference covering users, sudo, ACLs, special mode bits, SSH access, SELinux, and AppArmor basics.
Export
Copy the compact sheet, download it, or print it.
Download
`D` dense toggle · `C` copy all
Accounts Authentication and Access
Audit identities, SSH access, and authentication-related state.
bash
getent group dockerNotes
Useful when group data is not only in local `/etc/group`.
bash
sudo passwd -l deployNotes
Useful during account offboarding or incident response.
Show password aging info
Inspect account password expiration details.
bashLINUXchagepasswordsecurity
bash
sudo chage -l aliceNotes
Useful for compliance and access reviews.
bash
sudo visudoNotes
Always use `visudo` instead of editing sudoers directly.
bash
sudo sshd -tNotes
Run before restarting SSH to avoid locking yourself out.
bash
cat id_ed25519.pub >> ~/.ssh/authorized_keysNotes
Ensure permissions on `~/.ssh` and `authorized_keys` are strict.
Permissions ACLs and Special Bits
Go beyond rwx with ACLs, sticky bit, and setuid/setgid.
Set sticky bit on shared directory
Allow only owners to delete their own files in a shared directory.
bashLINUXchmodsticky-bitpermissions
bash
chmod +t /shared/tmpNotes
Common on world-writable directories like `/tmp`.
Set setgid on directory
Force new files to inherit the directory group.
bashLINUXchmodsetgidpermissions
bash
chmod g+s /srv/sharedNotes
Useful for team-shared directories.
bash
find / -perm -4000 -type f 2>/dev/nullNotes
Useful for security audits and hardening reviews.
Find world-writable paths
Audit files or directories writable by anyone.
bashLINUXfindpermissionssecurity
bash
find / -xdev -type d -perm -0002 2>/dev/nullNotes
Useful for security posture reviews.
Set default ACL on directory
Apply inherited ACL rules to new files and directories.
bashLINUXacldefaultpermissions
bash
setfacl -d -m g:appteam:rwx shared/Notes
Useful in team collaboration directories.
SELinux and AppArmor Basics
Inspect and work with Linux mandatory access control frameworks.
bash
getenforceNotes
Common first step on SELinux-enabled hosts.
bash
sestatusNotes
Provides more context than `getenforce`.
bash
sudo restorecon -Rv /var/www/htmlNotes
Very useful when copied files have wrong SELinux labels.
Allow service on custom SELinux port
Add or modify SELinux port context mapping.
bashLINUXselinuxportssecurity
bash
sudo semanage port -a -t http_port_t -p tcp 8080Notes
Required when services move to nonstandard ports on SELinux systems.
bash
sudo aa-statusNotes
Useful on Ubuntu and other AppArmor-enabled systems.
bash
journalctl -t audit --since '1 hour ago'Notes
Helpful when security policy blocks access and you need clues quickly.
More in Linux
Linux Networking Admin Cheat Sheet
Comprehensive Linux networking administration reference covering iproute2, DNS, HTTP debugging, TLS, SSH tunnels, packet capture, and firewall inspection.
Linux Shell Scripting Cheat Sheet
High-value Linux shell scripting reference covering variables, expansion, conditionals, loops, functions, redirection, pipelines, traps, getopts, and script debugging.
Linux Package Management Cheat Sheet
Comprehensive Linux package management reference for apt, dnf, yum, pacman, zypper, rpm, and dpkg workflows across common distributions.
Linux Command Cheat Sheet
Comprehensive Linux command reference covering navigation, files, text processing, permissions, processes, system information, networking, archives, services, storage, and troubleshooting.
Recommended next
Bash Scripting Patterns and Practical Recipes
BASH
Production-minded Bash script patterns for files, arguments, parsing, temp files, logging, retries, and common automation tasks.
Bash Builtins, Job Control, and Shell Behavior
BASH
Core Bash builtins, shell options, history, aliases, job control, traps, and interactive-shell behavior.
Bash Arrays, Strings, and Text Handling
BASH
Indexed and associative arrays, string handling, read/mapfile, and common Bash text-processing patterns.
Bash Conditionals, Loops, and Functions
BASH
Bash if/elif/case logic, test expressions, loops, functions, return codes, and robust control-flow patterns.
Bash Variables, Quoting, and Expansion
BASH
Bash variables, parameter expansion, quoting rules, command substitution, arithmetic, and shell expansion patterns.
Bash Cheat Sheet
BASH
Comprehensive Bash commands, shell syntax, quoting, variables, redirection, pipelines, and day-to-day scripting patterns.