How to Change File Permissions

Prerequisites

Before changing permissions, make sure you have:

• SSH access to your VPS
• Ownership of the file or sudo privileges

Understanding Linux Permissions

Connect to your VPS:

ssh hxroot@YOUR_SERVER_IP -p 22

View current permissions:

ls -l filename

Example output:

-rw-r--r-- 1 hxroot hxroot 1234 Apr 28 10:30 file.txt

Permission breakdown:

• - = file type (-=file, d=directory, l=symlink)
• rw- = owner permissions (read, write)
• r-- = group permissions (read only)
• r-- = others permissions (read only)

Permission Numbers (Octal)

Number	Permission
0	--- (no permissions)
1	--x (execute only)
2	-w- (write only)
3	-wx (write and execute)
4	r-- (read only)
5	r-x (read and execute)
6	rw- (read and write)
7	rwx (read, write, execute)

Format: chmod [owner][group][others] filename

Common chmod Examples

File permissions:

chmod 644 file.txt   # rw-r--r-- (default for files)
chmod 755 script.sh  # rwxr-xr-x (executable scripts)
chmod 600 private.txt # rw------- (private file)
chmod 640 config.conf # rw-r----- (owner+group)

Directory permissions:

chmod 755 directory  # drwxr-xr-x (default for directories)
chmod 700 private_dir # drwx------ (private directory)

Symbolic Mode (Letters)

Add execute permission for owner:

chmod u+x script.sh

Remove write permission for group:

chmod g-w file.txt

Add read for all users:

chmod a+r file.txt

Set exact permissions:

chmod u=rw,g=r,o=r file.txt

Recursive Permission Changes

Change entire directory tree:

chmod -R 755 /var/www/mysite/

Set directories to 755, files to 644 (find + chmod):

find /var/www -type d -exec chmod 755 {} ;
find /var/www -type f -exec chmod 644 {} ;

Web Server Best Practices

WordPress permissions:

find /var/www/html -type d -exec chmod 755 {} ;
find /var/www/html -type f -exec chmod 644 {} ;
chmod 660 /var/www/html/wp-config.php
chmod 775 /var/www/html/wp-content/uploads

Nginx/Apache files:

chown -R www-data:www-data /var/www/html/
chmod 755 /var/www/html/
chmod 644 /var/www/html/*.php

Security Best Practices

• config.php/files with passwords - 600 or 640
• Public files - 644
• Executable scripts - 755
• Upload directories - 755 (never 777)
• SSH keys - 600 (~/.ssh/id_rsa), 644 (~/.ssh/id_rsa.pub)

Special Permissions (SetUID, SetGID, Sticky Bit)

SetUID (run as owner):

chmod u+s /usr/bin/passwd

SetGID (inherit group):

chmod g+s /shared/directory

Sticky Bit (only owner can delete):

chmod +t /tmp

Check and Fix Permissions Script

#!/bin/bash
echo "Checking permission issues..."
find /var/www -type f -perm 777 -ls
find /var/www -type d -perm 777 -ls
echo "Fix dangerous permissions? (y/n)"
read answer
if [ "$answer" = "y" ]; then
    find /var/www -type f -perm 777 -exec chmod 644 {} ;
    find /var/www -type d -perm 777 -exec chmod 755 {} ;
    echo "Fixed"
fi