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NAME
setresuid, setresgid - set real, effective and saved user or group ID
SYNOPSIS
#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);
DESCRIPTION
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 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.
RETURN VALUE
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().
ERRORS
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 execve(2).
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 CAP_SETUID capability) and tried to change
the IDs to values that are not permitted.
VERSIONS
These calls are available under Linux since Linux 2.1.44.
CONFORMING TO
These calls are nonstandard; they also appear on HP-UX and some of the BSDs.
NOTES
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).
SEE ALSO
getresuid(2), getuid(2), setfsgid(2), setfsuid(2), setreuid(2), setuid(2), capabilities(7), credentials(7), user_namespaces(7)
COLOPHON
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