SETGID Section: Linux Programmer's Manual (2) Updated: 29 July 2025 Index   NAME setgid - set group identity   SYNOPSIS #include <unistd.h> int setgid(gid_t gid)   DESCRIPTION setgid sets the effective group ID of the current process. If the caller is the superuser, the real and saved group ID's are also set. Under Linux, setgid is implemented like the POSIX version with the _POSIX_SAVED_IDS feature. This allows a setgid (other than root) program to drop all of its group privileges, do some un-privileged work, and then re-engage the original effective group ID in a secure manner. If the user is root or the program is setgid root, special care must be taken. The setgid function checks the effective gid of the caller and if it is the superuser, all process related group ID's are set to gid. After this has occurred, it is impossible for the program to regain root privileges. Thus, a setgid-root program wishing to temporarily drop root privileges, assume the identity of a non-root group, and then regain root privileges afterwards cannot use setgid. You can accomplish this with the (non-POSIX, BSD) call setegid.   RETURN VALUE On success, zero is returned. On error, -1 is returned, and errno is set appropriately.   ERRORS EPERM The user is not the super-user, and gid does not match the effective or saved group ID of the calling process.   CONFORMING TO SVr4, SVID.   SEE ALSO   Index NAME SYNOPSIS DESCRIPTION RETURN VALUE ERRORS CONFORMING TO SEE ALSO This document was created by using the manual pages. Time: 11:56:07 GMT, March 24, 2025