Chmod

wikipedia:chmod command is used to change the access permissions including special mode flags (sticky) of files and directories

chmod examples

• chmod a+x /path/to/file.txt
• chmod og-r ~/.ssh/authorized_keys
• chmod og-rxw ~/.ssh

chmod ug+s /path/to/file.txt

Before:
ls -la file.txt
-rwxr-xr-x   1 root         root    31 Nov 27 11:34 file.txt

stat file.txt
  File: file.txt
  Size: 31        	Blocks: 8          IO Block: 4096   regular file
Device: fd00h/64768d	Inode: 13          Links: 1
Access: (0755/-rwxr-xr-x)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2019-11-27 11:34:54.610196393 +0400
Modify: 2019-11-27 11:34:49.662193415 +0400
Change: 2019-11-27 11:34:49.666193418 +0400
 Birth: -

chmod ug+s file.txt

After:
ls -la file.txt
-rwsr-sr-x 1 root root 31 Nov 27 11:34 file.txt

stat file.txt
  File: file.txt
  Size: 31        	Blocks: 8          IO Block: 4096   regular file
Device: fd00h/64768d	Inode: 13          Links: 1
Access: (6755/-rwsr-sr-x)  Uid: (    0/    root)   Gid: (    0/    root)
Access: 2019-11-27 11:34:54.610196393 +0400
Modify: 2019-11-27 11:34:49.662193415 +0400
Change: 2019-11-27 12:11:20.637362248 +0400
 Birth: -

See also

• sudo, id, visudo, useradd, userdel, usermod, groups, passwd, chown, chmod, chgrp, groupadd, groupdel, Passwordless sudo, passwd (package), sudo --help