chmod command

Examples

1. To add a type of permission to several files:

   chmod  g+w  chap1  chap2

   This adds write permission for group members to the files chap1 and chap2.
2. To make several permission changes at once:

   chmod  go-w+x  mydir

   This denies group members and others the permission to create or delete files in mydir (go-w) and allows group members and others to search mydir or use it in a path name (go+x). This is equivalent to the command sequence:

   chmod  g-w  mydir
   chmod  o-w  mydir
   chmod  g+x  mydir
   chmod  o+x  mydir

3. To permit only the owner to use a shell procedure as a command:

   chmod  u=rwx,go= cmd

   This gives read, write, and execute permission to the user who owns the file (u=rwx). It also denies the group and others the permission to access cmd in any way (go=).

   If you have permission to execute the cmd shell command file, then you can run it by entering:

   cmd

   Note: Depending on the PATH shell variable, you may need to specify the full path to the cmd file.
4. To use Set-ID Modes:

   chmod  ug+s  cmd

   When the cmd command is executed, the effective user and group IDs are set to those that own the cmd file. Only the effective IDs associated with the child process that runs the cmd command are changed. The effective IDs of the shell session remain unchanged.

   This feature allows you to permit access to restricted files. Suppose that the cmd program has the Set-User-ID Mode enabled and is owned by a user called dbms. The user dbms is not actually a person, but might be associated with a database management system. The user betty does not have permission to access any of dbms's data files. However, she does have permission to execute the cmd command. When she does so, her effective user ID is temporarily changed to dbms, so that the cmd program can access the data files owned by the user dbms.

   This way the user betty can use the cmd command to access the data files, but she cannot accidentally damage them with the standard shell commands.

5. To use the absolute mode form of the chmod command:

   chmod  644  text

   This sets read and write permission for the owner, and it sets read-only mode for the group and others. This also removes all extended ACLs that might be associated with the file.
6. To recursively descend directories and change file and directory permissions given the tree structure:

   ./dir1/dir2/file1

   ./dir1/dir2/file2

   ./dir1/file1

   enter this command sequence:

   chmod -R 777 f*

   which will change permissions on ./dir1/file1.

   But given the tree structure of:

   ./dir1/fdir2/file1

   ./dir1/fdir2/file2

   ./dir1/file3

   the command sequence:

   chmod -R 777 f*

   will change permissions on:

   ./dir1/fdir2

   ./dir1/fdir2/file1

   ./dir1/fdir2/file2

   ./dir1/file3