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# setreuid() - Unix, Linux System Call

# NAME

setreuid, setregid - set real and/or effective user or group ID

# SYNOPSIS

#include <sys/types.h>
#include <unistd.h>

int setreuid(uid_t ruid, uid_t euid);
int setregid(gid_t rgid, gid_t egid);

# DESCRIPTION

setreuid() sets real and effective user IDs of the current process.

Supplying a value of -1 for either the real or effective user ID forces the system to leave that ID unchanged.

Unprivileged processes may only set the effective user ID to the real user ID, the effective user ID or the saved set-user-ID.

POSIX: It is unspecified whether unprivileged processes may set the real user ID to the real user ID, the effective user ID or the saved set-user-ID.

Linux: Unprivileged users may only set the real user ID to the real user ID or the effective user ID.

Linux: If the real user ID is set or the effective user ID is set to a value not equal to the previous real user ID, the saved set-user-ID will be set to the new effective user ID.

Completely analogously, setregid() sets real and effective group ID’s of the current process, and all of the above holds with "group" instead of "user".

# RETURN VALUE

On success, zero is returned. On error, -1 is returned, and errno is set appropriately.

# ERRORS

Tag | Description
--- | ---
EPERM | The current process is not privileged (Linux: does not have the CAP_SETUID capability in the case of setreuid(), or the CAP_SETGID capability in the case of setregid()) and a change other than (i) swapping the effective user (group) ID with the real user (group) ID, or (ii) setting one to the value of the other or (iii) setting the effective user (group) ID to the value of the saved set-user-ID (saved set-group-ID) was specified.

# NOTES

Setting the effective user (group) ID to the saved set-user-ID (saved set-group-ID) is possible since Linux 1.1.37 (1.1.38).

# CONFORMING TO

POSIX.1-2001, 4.3BSD (the setreuid() and setregid() function calls first appeared in 4.2BSD).

# SEE ALSO

- getgid (2)

- getuid (2)

- seteuid (2)

- setgid (2)

- setresuid (2)

- setuid (2)

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