What is the command used to add SUID permissions in Linux?

Adding SUID (Set Owner User ID) permissions in Linux allows users to execute a file with the permissions of the file's owner rather than the permissions of the user running the file. This is particularly useful for allowing ordinary users to execute programs that require elevated privileges, such as changing their passwords.

To set SUID permissions, you would use the command syntax that involves the chmod command combined with a +s option after the permissions set. When you use chmod, you can indicate the SUID bit specifically by using a lowercase "s." For example, if you wanted to set SUID on a file named example, you would run chmod u+s example. This command adds the SUID permission, thereby allowing the file to be executed with the privileges of its owner.

The other options do not pertain to SUID permissions specifically. The +x option is used to add execute permissions, +a does not correspond to a standard file permission modification command in Linux, and +w is used to add write permissions. Thus, only +s correctly represents the command used to modify file permissions to include the SUID bit.