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

       These calls are available under Linux since Linux 2.1.44.

STANDARDS

       These calls are nonstandard; they also appear on HP-UX and some of the BSDs.

NOTES

       Under HP-UX and FreeBSD, the prototype is found in <unistd.h>.  Under Linux, the prototype
       is provided since glibc 2.3.2.

       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.

   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).

SEE ALSO

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