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


       #define _GNU_SOURCE
       #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.

       Unprivileged user processes may change the 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.

       Privileged processes (on Linux, those having the CAP_SETUID capability)
       may set the 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 file system 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
       file  system  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.


       EAGAIN uid  does  not  match  the current UID and this call would bring
              that user ID over its RLIMIT_NPROC resource limit.

       EPERM  The  calling  process  is  not  privileged  (did  not  have  the
              CAP_SETUID  capability)  and  tried  to change the IDs to values
              that are not permitted.


       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.


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


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