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) */
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
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 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 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), capabili-
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Linux 2010-11-22 SETRESUID(2)