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Linux Permissions (Hardening) Cheat Sheet by

A simple checklist for Linux permission when performing hardening.

Ownership & Permis­sions

Command
Purpose
 
ls -l
View permis­sions
 
stat FILE
Detailed file info
 
chmod MODE FILE
Change permis­sions
 
chown USER FILE
Change owner
 
chgrp GROUP FILE
Change group
 
umask
View default permis­sions
 
umask 022
Set default permis­sions

Common Permission Values

600
Owner RW
644
Owner RW, Others R
700
Owner RWX
755
Owner RWX, Others RX
777
Everyone RWX (Avoid)
 

ACL (Access Control Lists)

Command
Purpose
 
getfacl FILE
View ACL
 
setfacl -m u:USER:rwx FILE
Add ACL
 
setfacl -x u:USER FILE
Remove ACL
 
setfacl -b FILE
Remove all ACLs

Attributes

Command
Purpose
 
lsattr
View attributes
 
chattr +i FILE
Immutable
 
chattr -i FILE
Remove immutable
 
chattr +a FILE
Append only

Reference Box

r = Read
w = Write
x = Execute

4 = Read
2 = Write
1 = Execute

------­---­---­---­---­------

SUID = Run as Owner
SGID = Run as Group
Sticky = Only Owner Can Delete
 

SUID / SGID

Command
Purpose
 
find / -perm -4000
Find SUID files
 
find / -perm -2000
Find SGID files
 
chmod u-s FILE
Remove SUID
 
chmod g-s FILE
Remove SGID

Sticky Bit

Command
Purpose
 
chmod +t DIR
Set Sticky Bit
 
chmod -t DIR
Remove Sticky Bit

Security Checklist

Least Privilege
Avoid chmod 777
Secure ~/.ssh (700)
Secure private keys (600)
Protect /etc/s­hadow
Audit SUID files
Review ownership
 

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  • Published: 7th August, 2026

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