Linux group permission

Group permissions

the file.
World permissions

neither the UID nor the GID of the file. In addition to being called world permissions,

they are also called other permissions.

Each of these groups can be granted any combination of three possible permissions:
Read permission
Write permission
Execute permission

Use the –l option with the ls command to view the ownership and permissions assigned to a file.

Listing 9.1: Examining File Permissions with ls

$ ls −l

total 1641

−rw−r−−r−− 1 craig users 8255 May 17 14:09 fig2−1.gif

−rw−r−−r−− 1 craig users 8206 May 17 14:10 fig2−2.gif

−rw−r−−r−− 1 craig users 16328 May 16 22:04 fig3−2.gif

−rw−r−−r−− 1 craig users 3832 May 16 22:13 fig4−1.gif

−rw−r−−r−− 1 craig users 16741 May 16 22:18 fig4−2.gif

−rw−r−−r−− 1 craig users 14350 May 16 22:24 fig4−4.gif

−rw−r−−r−− 1 craig users 22737 May 16 22:27 fig4−5.gif

−rw−r−−r−− 1 craig users 14316 May 16 22:34 fig5−1.gif

−rw−r−−r−− 1 craig users 15739 May 16 22:35 fig5−2.gif

−rw−r−−r−− 1 craig users 21528 May 1 20:46 fig8−1.gif

−rw−r−−r−− 1 craig users 16479 May 1 21:18 fig8−2.gif

−rw−r−−r−− 1 craig users 22295 May 17 11:43 fig8−4.gif

−rw−r−−r−− 1 craig users 16482 Apr 24 19:50 fig9−3.gif

−rw−r−−r−− 1 craig users 11756 Apr 24 19:54 fig9−4.gif

Each line in the long format directory listing begins with the file permissions. The first 10 characters

are the same for every file in Listing 9.1: –rw−r−−r−−. The very first character indicates whether this

is a directory (d), a link (l), or a file (−). In the example, all of the entries are files.

The next nine characters are divided into three groups of three to define the permissions for the

owner of the file, for the members of the group to which this file is assigned, and for all other users.

An r in the permission field indicates read permission, a w indicates write, and an x indicates

execute.

In Listing 9.1, the owner is granted read and write permissions (rw−), and everyone else— members

of the group as well as other users of the system—are granted only read access (r−−).

The permissions can be viewed as three 3−bit numbers. r is 4 (binary 100), w is 2 (binary 010), and

x is 1 (binary 001). Thus, the permission granted to the owner in Listing 9.1 is 6 (rw−), and the

permissions granted to the group and to the world are 4 (r−−) for a file permission setting of 644.

The program contained in the file may be executed.The contents of the file may be modified.The contents of the file may be examined.The permissions granted to all other users, those who haveThe permissions granted to users who have the same GID as