|SETFSUID(2)||Linux Programmer's Manual||SETFSUID(2)|
NAMEsetfsuid - set user identity used for file system checks
SYNOPSIS#include <unistd.h> /* glibc uses <sys/fsuid.h> */
DESCRIPTIONThe system call setfsuid() sets the user ID that the Linux kernel uses to check for all accesses to the file system. Normally, the value of fsuid will shadow the value of the effective user ID. In fact, whenever the effective user ID is changed, fsuid will also be changed to the new value of the effective user ID.
RETURN VALUEOn success, the previous value of fsuid is returned. On error, the current value of fsuid is returned.
VERSIONSThis system call is present in Linux since version 1.2.
CONFORMING TOsetfsuid() is Linux-specific and should not be used in programs intended to be portable.
NOTESWhen glibc determines that the argument is not a valid user ID, it will return -1 and set errno to EINVAL without attempting the system call.
Note that at the time this system call was introduced, a process could send a signal to a process with the same effective user ID. Today signal permission handling is slightly different.
The original Linux setfsuid() system call supported only 16-bit user IDs. Subsequently, Linux 2.4 added setfsuid32() supporting 32-bit IDs. The glibc setfsuid() wrapper function transparently deals with the variation across kernel versions.
BUGSNo error messages of any kind are returned to the caller. At the very least, EPERM should be returned when the call fails (because the caller lacks the CAP_SETUID capability).
SEE ALSOkill(2), setfsgid(2), capabilities(7), credentials(7)
COLOPHONThis page is part of release 3.53 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.