Format
Use ls -l to see permissions, you’ll see file/dir have the following format: _rwxrwxrwx
The first character can be marked with any of the following:
- _ - no special permissions
- d - directory
- l - the file or directory is a symbolic link
- s - setuid/setgid. This will let the system run an executable as the owner with the owner’s permissions
- t - sticky bit permission. This will only let the file owner rename or delete the said file.
The second group of 3 characters represent what the owner of this file can do.
The third group of 3 characters represent what the owner group of this file can do.
The fourth group of 3 characters represent what all users can do.
Permission Groups
- owner(u)
- group(g)
- all users(a), including owner + group
- all other users(o)
Use ls -ld file / stat file to find the user & group of the file
Modify ownership:
chmod a+rw file1 add read and write permission to file1 for all users
chmod g-x file2 remove execution permission to file2 for group
chmod u=rwx file1 set owner permission of file1 to be rwx
chmod -R u=rwx file1 -R = recursively set
chmod u+w,g+x,o-r set multiple permissions together
chmod u=rwx,g=rw,o=rx file set multiple permissions together
Assign ownership: chown owner filename / chgrp groupname filename
Permission Types
- read = 4(100)
- write = 2(010)
- execute = 1(001)
You add the numbers to get the integer/number representing the permissioons. For example:
_rwxr_xr__ = 111101100 = (4+2+1)(4+1)(4) = 754
To change permission type for this file: chmod 754 file