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The rmdir command looks like this:

[user@dhcppc1 user]$ ls /home/user Desktop/ mydir/ myfile2 nsmail/ tmp/

[user@dhcppc1 user]$ rmdir --verbose /home/user/mydir rmdir: removing directory, /home/user/mydir [user@dhcppc1 user]$ ls /home/user

Desktop/ myfile2 nsmail/ tmp/

Setting File and Directory Permissions

4.4 Identify and change file permissions, modes and types by using chmod, chown and chgrp

Administrators not only have to navigate files and directories, they must also control access to these files and directories. To do this, the administrator must use several commands to restrict file and directory use. For example, log in as a standard user and then attempt to cd into the /root or another user directory. Attempting this action returns the following information:

[user@dhcppc1 user]$ cd /root bash: cd: /root: Permission denied [user@dhcppc1 user]$

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This information shows that the /root directory has permissions that deny most users from having access, as shown in the following:

This information shows that the root directory is not available to anyone but the root user. To change the permissions to a file or directory, use several tools, such as chmod, chown and chgrp, to control access.

The chmod command

The chmod command enables you to change file access permissions in Linux. This command uses the following format: chmod [OPTION]... {MODE | --reference=FILE} FILE, and can use OCTAL-MODE instead of MODE, with the symbolic mode format shown as [ugoa...][[+-=][rwxXstugo...]...][,...].

The following characters, shown with the meaning of their letters and symbols, select the new permissions for the file or directory:

Owner types

u = The user who owns it

g = Other users in the file’s group

o = Other users not in the file’s group

a = All users

Permission actions

+ = Selected permissions are added to the existing permissions of each file

- = Selected permissions are removed from the existing permissions of each file

= = Selected permissions are assigned as the only permissions of each file

Permission types

r = Read

w = Write

x = Execute for files or access for directories

X = Execute only if the file is a directory or already has execute permission for some user

s = Sets user or group ID on execution

t = Saves program text on swap device

u = The permissions that the user who owns the file currently has for the file

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g = The permissions that other users in the file’s group have for the file

o = The permissions that other users, not in the file’s group, have for the file

a = All users

The octal uses 4 bits (0-7) represented as 4, 2, and 1 (adds to 7), with the first digit used to set the user ID (4), group ID (2), or save the text image attributes (1). The second digit is used to select permissions for the user who owns the file, the third digit is used to select permissions for other users in the file’s group, and the fourth digit is used to select the permissions for other users not in the file’s group; all use 4 for read, 2 for write, and 1 for execute. The chmod command also uses the options shown in Table 9-13.

The basic use of the chmod command looks similar to the following:

[user@dhcppc1 user]$ chmod --verbose 4420 myfile mode of myfile changed to 4420 (r-S-w----) [user@dhcppc1 user]$

This command can be used to change the permissions on directories, as well as files, and should be used with care because it may cause access issues if used improperly.

The chown command

Use the chown command to change the user and/or group ownership of each listed \ file, which you can do by taking the first non-option argument in the standard

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format of the chmod command — chown [OPTION]... OWNER[.[GROUP]] FILE. If the first option is only a user name, or UID, then that user is made the owner of all files listed. If the user name is followed by a colon or period and a group name with no spaces, then the group ownership is also changed. If no group is included, but the colon (:) or period (.) is included, then the user’s login group is assigned group ownership. This command can also omit the user name and include only the period or colon and group to change the group ownership of the files listed; this is the same function as chgrp. The options available to the chown command are shown in Table 9-14.

The chown command often looks like the following (for the file ‘newfile’, created by user, in the directory /tmp):

[root@dhcppc1 /home]# chown --verbose user2 /tmp/newfile owner of /tmp/newfile changed to user2

The chgrp command

The change group command uses the following format: chgrp [options] GROUP FILE. This command works very similarly to the chown command, but is used to only change group ownership of a file. The chgrp command uses the same options