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       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.

       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-

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


       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 BSDs.


       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.


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


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