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


   #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);


   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

   If one of the arguments equals  -1,  the  corresponding  value  is  not

   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.


   On success, zero is returned.  On error, -1 is returned, and  errno  is
   set appropriately.

   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().


   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

   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


   These calls are available under Linux since Linux 2.1.44.


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


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


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


   This page is part of release 4.09 of the Linux  man-pages  project.   A
   description  of  the project, information about reporting bugs, and the
   latest    version    of    this    page,    can     be     found     at

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