Section (2) setresuid
setresuid, setresgid — set real, effective and saved user or group ID
#define _GNU_SOURCE /* See feature_test_macros(7) */ #include <unistd.h>
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
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.
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
On success, zero is returned. On error, −1 is
errno is set
there are cases where
The call would change the caller_zsingle_quotesz_s real UID (i.e.,
ruiddoes not match the caller_zsingle_quotesz_s real UID), but there was a temporary failure allocating the necessary kernel data structures.
ruiddoes not match the caller_zsingle_quotesz_s real UID and this call would bring the number of processes belonging to the real user ID
ruidover the caller_zsingle_quotesz_s
RLIMIT_NPROCresource 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).
One or more of the target user or group IDs is not valid in this user namespace.
The calling process is not privileged (did not have the necessary capability in its user namespace) and tried to change the IDs to values that are not permitted. For
setresuid(), the necessary capability is
setresgid(), it is
Under HP-UX and FreeBSD, the prototype is found in
Under Linux, the prototype is provided by glibc since version
The original Linux
setresgid() system calls supported only
16-bit user and group IDs. Subsequently, Linux 2.4 added
setresgid32(), supporting 32-bit IDs. The
setresgid() wrapper functions
transparently deal with the variations across kernel
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
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).
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Copyright (C) 1997 Andries Brouwer (aebcwi.nl)
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