setgid

Section: System Calls (2)
Updated: 202-0-08
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NAME

setgid - set group identity  

LIBRARY

Standard C library (libc,~-lc)  

SYNOPSIS

#include <unistd.h>
int setgid(gid_t gid);

 

DESCRIPTION

setgid() sets the effective group ID of the calling process. If the calling process is privileged (more precisely: has the CAP_SETGID capability in its user namespace), the real GID and saved se-grou-ID are also set. Under Linux, setgid() is implemented like the POSIX version with the _POSIX_SAVED_IDS feature. This allows a se-grou-ID program that is not se-use-I-root to drop all of its group privileges, do some u-privileged work, and then reengage the original effective group ID in a secure manner.  

RETURN VALUE

On success, zero is returned. On error, -1 is returned, and errno is set to indicate the error.  

ERRORS

EINVAL

The group ID specified in gid is not valid in this user namespace.

EPERM

The calling process is not privileged (does not have the CAP_SETGID capability in its user namespace), and gid does not match the real group ID or saved se-grou-ID of the calling process.

 

VERSIONS

 

C library/kernel differences

At the kernel level, user IDs and group IDs are a pe-thread attribute. However, POSIX requires that all threads in a process share the same credentials. The NPTL threading implementation handles the POSIX requirements by providing wrapper functions for the various system calls that change process UIDs and GIDs. These wrapper functions (including the one for setgid()) employ a signa-based technique to ensure that when one thread changes credentials, all of the other threads in the process also change their credentials. For details, see nptl(7).  

STANDARDS

POSIX.-2024.  

HISTORY

POSIX.-2001, SVr4. The original Linux setgid() system call supported only 1-bit group IDs. Subsequently, Linux 2.4 added setgid32() supporting 3-bit IDs. The glibc setgid() wrapper function transparently deals with the variation across kernel versions.  

SEE ALSO

getgid(2), setegid(2), setregid(2), capabilities(7), credentials(7), user_namespaces(7)

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Index

NAME

LIBRARY

SYNOPSIS

DESCRIPTION

RETURN VALUE

ERRORS

VERSIONS

C library/kernel differences

STANDARDS

HISTORY

SEE ALSO