capng_set_rootid - Linux


capng_set_rootid is a Linux command used for setting the real user ID (RUID) of the current process and is primarily useful for dropping root privileges or changing the effective user ID. It’s commonly employed in security-sensitive contexts, such as privilege separation.


capng_set_rootid [OPTIONS] ID


  • -h, –help: Displays the help message.
  • -v, –version: Outputs the command version.


Dropping Root Privileges

To drop root privileges to user with ID 1000:

capng_set_rootid 1000

Changing Effective User ID

To change the effective user ID to 1000:

capng_set_rootid --set-effective 1000

Common Issues

Error: Operation not permitted: Ensure that the current process has sufficient privileges (e.g., running as root) to change the RUID.


capng_set_rootid can be combined with other commands to enhance security posture, such as:

  • setfacl: Set file access control lists for specific users/groups.
  • chroot: Change the root directory of the current process, isolating it from the rest of the system.

Related Commands

  • setuid
  • getuid
  • capng_get_caps