Linux Permissions and Links Cheat Sheet

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Change permissions, ownership, umask, and symbolic or hard links on Linux.

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## chmod Basics

Add execute permission for user

↗#

chmod u+x script.sh

# Grant user execute permission.

Set file to 644

↗#

chmod 644 config.ini

# Common mode for normal text or config files.

Set file or directory to 755

↗#

chmod 755 deploy.sh

# Common executable/script or directory mode.

Change permissions recursively

↗#

chmod -R u=rwX,go=rX project

# Apply mode changes to a directory tree.

## Ownership and umask

Change owner and group

↗#

sudo chown alice:developers app.log

# Set file owner and group together.

Recursively change ownership

↗#

sudo chown -R www-data:www-data /var/www/app

# Update owner and group across a tree.

Change group

↗#

chgrp developers shared.txt

# Set a file's group without changing owner.

Show and set umask

↗#

umask && umask 027

# Inspect and change default permission mask.

## Special Permission Bits

Set setuid bit

↗#

chmod u+s binary

# Set executable to run with owner's effective UID.

Set setgid on directory

↗#

chmod g+s shared-dir

# New files inherit directory group.

Set sticky bit on directory

↗#

chmod +t /shared/tmp

# Allow only owners/root to delete their own files.

## Links and Link Recipes

Replace symlink atomically-ish

↗#

ln -sfn /opt/releases/2026-03-07 current

# Create or update a symlink target with force.

Find files sharing same inode count

↗#

find . -type f -links +1 -ls

# Inspect hard link count with ls/stat.

Inspect path components

↗#

namei -l /var/www/current/public

# Resolve each path component and symlink along the path.

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