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.

HISTORY

       Linux 2.1.44, glibc 2.3.2.  HP-UX, FreeBSD.

       The  original  Linux  setresuid()  and setresgid() system calls supported only 16-bit user and group IDs.
       Subsequently, Linux 2.4  added  setresuid32()  and  setresgid32(),  supporting  32-bit  IDs.   The  glibc
       setresuid()  and  setresgid()  wrapper  functions  transparently  deal  with the variations across kernel
       versions.

SEE ALSO

       getresuid(2),   getuid(2),   setfsgid(2),   setfsuid(2),   setreuid(2),    setuid(2),    capabilities(7),
       credentials(7), user_namespaces(7)