Linux Permissions and Security Cheat Sheet

getent passwd alice

# Resolve user information through NSS.

getent group docker

# Resolve group entries through NSS.

sudo passwd -l deploy

# Disable password authentication for a user.

sudo chage -l alice

# Inspect account password expiration details.

sudo visudo

# Open sudoers with syntax checking and locking.

sudo sshd -t

# Validate SSH daemon configuration for syntax errors.

cat id_ed25519.pub >> ~/.ssh/authorized_keys

# Append a key to authorized_keys.

chmod +t /shared/tmp

# Allow only owners to delete their own files in a shared directory.

chmod g+s /srv/shared

# Force new files to inherit the directory group.

find / -perm -4000 -type f 2>/dev/null

# Search for files with the setuid bit set.

find / -xdev -type d -perm -0002 2>/dev/null

# Audit files or directories writable by anyone.

setfacl -d -m g:appteam:rwx shared/

# Apply inherited ACL rules to new files and directories.

getenforce

# Print current SELinux mode.

sestatus

# Display SELinux policy and mode details.

sudo restorecon -Rv /var/www/html

# Reset file labels according to policy.

sudo semanage port -a -t http_port_t -p tcp 8080

# Add or modify SELinux port context mapping.

sudo aa-status

# Display loaded AppArmor profiles.

journalctl -t audit --since '1 hour ago'

# Query audit-related journal entries.