Every user on a Unix/Linux system has a unique username, and is a member of at least one group. This group information is held in the password file stored in /etc/passwd. A user can also be a member of one or more other groups, stored in /etc/group. Only the administrator can create new groups or add/delete group members.
Every directory and file on the system has an owner, and also an associated group. It also has a set of permission flags which specify separate read, write and execute permissions for the owner, group and other.
ls -l command shows the permissions and group associated with files.
ls -g command shows the group information.
The permission flags are read as follows (left to right)
1 | directory flag, 'd' if a directory, '-' if a normal file, something else occasionally may appear here for special devices. |
2,3,4 | read, write, execute permission for User (Owner) of file |
5,6,7 | read, write, execute permission for Group |
8,9,10 | read, write, execute permission for Other |
- | in any position means that flag is not set |
r | file is readable by owner, group or other |
w | file is writeable. On a directory, write access means you can add or delete files |
x | file is executable - only for programs and shell scripts. Execute permission on a directory means you can list the files in that directory |
