Lamp Chapter3

FOSS / LAMP Session 3

Revathi J Bharathidasan University Technology Park (BUTP) Bharathidasan University

Special permissions • A fourth permission user/group/other)

set

(in

addition

to

• Applicable in four cases:

Set user ID or suid for an executable Set group ID or sgid for an executable Set group ID or sgid for a directory Sticky bit for a directory

• Use the chmod command, preceeding the usual three digits with a digit representing the special permission : 4 for suid, 2 for sgid, 1 for the sticky bit.

Special Permissions for Executables • The Set UID Permission • Suid : Command run with permissions of the owner of the command, not exexcutor of the command • In long listing, the suid permission is displayed as a lower case “s” where the “x” would otherwise be located for the user permission.

Example - SUID • Create a new file $ touch su1

• To view the permission $ ls -l su1

• To set SUID permission $ chmod 4777 su1

• To view the modified permission $ ls -l su1

Set gid command • sgid : files created in directories with the sgid bit set have group affiliations of the group of the directory. • This is commonly used on group directories: $ chmod 2770 $ ls –l groupdir

Example • Create group

groupadd colleges

• Create users of the group useradd -G colleges jmc useradd -G colleges hcc

• Create group directory mkdir /csdata

• Assign group directory to a group chgrp colleges /csdata

• Create SGUID for group directory chmod 2770 /csdata

Special Permissions for Directories • Sticky Bit Files and directories with the sticky bit set can only be removed by the owner and root, regardless of the write permissions of the directory.

• For group directory /csdata, to set a Sticky bit chmod 3770 /csdata

Thank You