# setresuid

## NAME



           setresuid, setresgid - set real, effective, and saved user or
           group ID
    


## LIBRARY



           Standard C library (_libc_ , _-lc_)
    


## SYNOPSIS



           **#define _GNU_SOURCE** /* See feature_test_macros(7) */
           **#include <unistd.h>**
    
           **int setresuid(uid_t** _ruid_**, uid_t** _euid_**, uid_t** _suid_**);**
           **int setresgid(gid_t** _rgid_**, gid_t** _egid_**, gid_t** _sgid_**);**
    


## DESCRIPTION



           **setresuid**() sets the real user ID, the effective user ID, and the
           saved set-user-ID of the calling process.
    
           An unprivileged process may change its real UID, effective UID,
           and saved set-user-ID, each to one of: the current real UID, the
           current effective UID, or the current saved set-user-ID.
    
           A privileged process (on Linux, one having the **CAP_SETUID**
           capability) may set its real UID, effective UID, and saved set-
           user-ID to arbitrary values.
    
           If one of the arguments equals -1, the corresponding value is not
           changed.
    
           Regardless of what changes are made to the real UID, effective
           UID, and saved set-user-ID, the filesystem UID is always set to
           the same value as the (possibly new) effective UID.
    
           Completely analogously, **setresgid**() sets the real GID, effective
           GID, and saved set-group-ID of the calling process (and always
           modifies the filesystem GID to be the same as the effective GID),
           with the same restrictions for unprivileged processes.
    


## RETURN VALUE



           On success, zero is returned.  On error, -1 is returned, and _errno_
           is set to indicate the error.
    
           _Note_ : there are cases where **setresuid**() can fail even when the
           caller is UID 0; it is a grave security error to omit checking for
           a failure return from **setresuid**().
    


## ERRORS



           **EAGAIN** The call would change the caller's real UID (i.e., _ruid_
                  does not match the caller's real UID), but there was a
                  temporary failure allocating the necessary kernel data
                  structures.
    
           **EAGAIN** _ruid_ does not match the caller's real UID and this call
                  would bring the number of processes belonging to the real
                  user ID _ruid_ over the caller's **RLIMIT_NPROC** resource limit.
                  Since Linux 3.1, this error case no longer occurs (but
                  robust applications should check for this error); see the
                  description of **EAGAIN** in execve(2).
    
           **EINVAL** One or more of the target user or group IDs is not valid in
                  this user namespace.
    
           **EPERM** The calling process is not privileged (did not have the
                  necessary capability in its user namespace) and tried to
                  change the IDs to values that are not permitted.  For
                  **setresuid**(), the necessary capability is **CAP_SETUID** ; for
                  **setresgid**(), it is **CAP_SETGID**.
    


## VERSIONS



       **C library/kernel differences**
           At the kernel level, user IDs and group IDs are a per-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 those for **setresuid**() and
           **setresgid**()) employ a signal-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



           None.
    


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