Set real and effect user IDs
#include <unistd.h> int setreuid( uit_t ruid, uid_t euid );
Use the -l c option to qcc to link against this library. This library is usually included automatically.
The setreuid() function sets the real and effective user IDs of the calling process. If ruid or euid is -1, the corresponding real or effective user ID isn't changed.
If the effective user ID of the calling process is the superuser, you can set the real user ID and the effective user ID to any legal value.
If the effective user ID of the calling process isn't the superuser, you can set either the real user ID to the effective user ID, or the effective user ID to the saved set-user ID or the real user ID.
|If a set-UID process sets its effective user ID to its real user ID, it can still set its effective user ID back to the saved set-UID.|
In either case, if you're changing the real user ID (i.e. ruid is not -1), or you're changing the effective user ID to a value that isn't equal to the real user ID, the saved set-user ID is set equal to the new effective user ID.
The “superuser” is defined as any process with an effective user ID of 0, or an effective user ID of root.
Zero on success, or -1 if an error occurs (errno is set).
The calling process isn't the superuser, and you tried to change the real user ID to a value other than the effective user ID.
POSIX 1003.1 XSI
execve(), getuid(), setregid(), setuid()