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SETRESUID(2) Linux Programmer's Manual SETRESUID(2)


     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 neces-
            sary capability in its user namespace) and tried to  change  the
            IDs to values that are not permitted.  For setresuid(), the nec-
            essary capability is CAP_SETUID; for setresgid(), it is CAP_SET-


     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  setre-
     suid32()  and  setresgid32(),  supporting 32-bit IDs.  The glibc setre-
     suid() 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 4.16 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

Linux 2017-09-15 SETRESUID(2)

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