Manpage of SETRESUID
SETRESUIDSection: Linux Programmer's Manual (2)
NAMEsetresuid, setresgid - set real, effective and saved user or group ID
SYNOPSIS#define _GNU_SOURCE /* See feature_test_macros(7) */
DESCRIPTIONsetresuid() 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 VALUEOn success, zero is returned. On error, -1 is returned, and errnois set appropriately.
- The call would change the caller's real UID (i.e., ruiddoes not match the caller's real UID), but there was a temporary failure allocating the necessary kernel data structures.
- ruiddoes not match the caller's real UID and this call would bring the number of processes belonging to the real user ID ruidover the caller'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 EAGAINin 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 CAP_SETUIDcapability) and tried to change the IDs to values that are not permitted.
VERSIONSThese calls are available under Linux since Linux 2.1.44.
CONFORMING TOThese calls are nonstandard; they also appear on HP-UX and some of the BSDs.
NOTESUnder 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 differencesAt 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 ALSOgetresuid(2), getuid(2), setfsgid(2), setfsuid(2), setreuid(2), setuid(2), capabilities(7), credentials(7), user_namespaces(7)
- RETURN VALUE
- CONFORMING TO
- SEE ALSO
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