400r-------- (Owner read only)
600rw------- (Owner read/write)
644rw-r--r-- (Owner read/write, Group/Others read)
700rwx------ (Owner read/write/execute)
755rwxr-xr-x (Owner full, Group/Others read/execute)
775rwxrwxr-x (Group/Others read/execute)
777rwxrwxrwx (Everyone full access)
666rw-rw-rw- (Everyone read/write)
u+xAdd execute for user
g-wRemove write for group
o=rSet read only for others
a+xAdd execute for all
u=rwx,g=rx,o=Set owner rwx, group rx, others none
+xAdd execute to all
-xRemove execute from all
4755rwsr-xr-x (Setuid)
2755rwxr-sr-x (Setgid)
1755rwxr-xr-t (Sticky bit)
chmod 755 fileSet rwxr-xr-x permissions
chmod -R 644 dirRecursively set permissions
chmod u+x,g-w fileSymbolic mode changes
chmod +x script.shMake script executable
chmod 600 ~/.ssh/id_rsaSecure private key
chmod go-rwx fileRemove all permissions for group/others
r (4)Read permission
w (2)Write permission
x (1)Execute permission
4+2+1 = 7rwx (full permissions)
4+2 = 6rw- (read and write)
4+1 = 5r-x (read and execute)
4r-- (read only)