Su Must Be Suid To Work Properly Link Jun 2026

There are several ways to resolve this depending on your environment.

The SUID bit is a special permission bit on executable files that allows users to execute the file with the permissions of the file's owner. When the SUID bit is set on a program, users executing the program do so with the permissions of the program's owner, not their own. This allows system administrators to control which users can perform specific tasks that require higher privileges.

It is worth noting that on some systems, su might rely on the SGID (Set Group ID) bit to the shadow or root group rather than full SUID root. However, this is configuration-dependent. The most universal mechanism remains SUID root, as root is the only UID capable of switching to any other user ID freely.

The su command is designed to let a user become another user, most commonly . To perform this action securely, the program must do two things that a normal user is not allowed to do: su must be suid to work properly

To understand why su needs special treatment, we first need to understand how normal programs operate.

Without SUID:

: The primary purpose of su is to allow users to assume the identity of another user, usually to gain elevated privileges. If su were not SUID, users would not be able to switch to a different user account (such as root) because they wouldn't have the necessary permissions to do so. There are several ways to resolve this depending

Beyond the mechanics of switching users, su also needs SUID permissions to perform its most sensitive task: reading the password database.

Both require the SUID bit to break the barrier between the unprivileged caller and the privileged system state.

This "default denial" is the bedrock of multi-user security. If alice could run a program that simply declared, "I want to be root now," without a mechanism trusted by the kernel, the entire permission system would collapse. This allows system administrators to control which users

Attempt to use su :

ls -l /etc/shadow -rw-r----- 1 root shadow 1312 Oct 10 10:00 /etc/shadow

When a user launches an SUID binary: