Commands Linux

File Permissions

Commands for managing file and directory permissions, ownership, and special permission bits

File Permissions

chmod [mode] [file]

  • Changes file/directory permissions
  • Modes: numeric (755) or symbolic (u+x)

chown [user]:[group] [file]

  • Changes file ownership
  • Use : to separate user and group

chgrp [group] [file]

  • Changes group ownership only

Permission Modes

chmod 755 [file]

  • rwxr-xr-x (owner: rwx, others: rx)

chmod u+x,g-w,o=r [file]

  • Add execute for user, remove write for group
  • Set read-only for others

chmod -R 644 [directory]

  • Recursive permission change
  • rw-r–r– for all files in directory

Special Permissions

chmod +t [directory]

  • Sets sticky bit (typically /tmp)

chmod u+s [file]

  • Sets SUID bit

chmod g+s [directory]

  • Sets SGID bit

Verification

ls -l [file]

  • Shows detailed permissions
  • Format: -rwxrwxrwx owner group

stat [file]

  • Detailed file information
  • Octal and symbolic permissions

namei -l [path]

  • Shows permissions for entire path

Default Permissions

umask

  • Shows current umask value
  • Default permissions for new files

umask 022

  • Sets umask (subtracts from 666/777)

Example 

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# Set web directory permissions
sudo chown -R www-data:www-data /var/www
sudo chmod -R 755 /var/www
sudo chmod -R 644 /var/www/*.html

# Make script executable
chmod +x script.sh