SUSER(9) MidnightBSD Kernel Developer’s Manual SUSER(9)


suser, suser_cred — check if credentials have superuser privileges


#include <sys/priv.h>


suser(struct thread *td);


suser_cred(struct ucred *cred, int flag);


The suser() and suser_cred() functions check if the credentials given include superuser powers.

These interfaces have now been obsoleted by priv(9), and are provided only for compatibility with third party kernel modules that have not yet been updated to the new interface. They should not be used in any new kernel code.

The suser() function is the most common, and should be used unless special circumstances dictate otherwise.

The suser_cred() function should be used when the credentials to be checked are not the thread’s own, when there is no thread, when superuser powers should be extended to imprisoned roots, or when the credential to be checked is the real user rather than the effective user.

Whether or not a privilege is permitted in a jail(8) depends on logic in prison_priv_check().

In general, privileges are assigned based on the effective user ID; in some cases, the real user ID may be used.

The flags field is currently unused.

The suser() and suser_cred() functions note the fact that superuser powers have been used in the process structure of the process specified. Because part of their function is to notice whether superuser powers have been used, the functions should only be called after other permission possibilities have been exhausted.


The suser() and suser_cred() functions return 0 if the user has superuser powers and EPERM otherwise. This is the reverse logic of some other implementations of suser() in which a TRUE response indicates superuser powers.


chroot(2), jail(2), priv(9)


The suser() and suser_cred() functions do not, in fact, record that superuser privileges have been used, and have not done so since August 2000.

MidnightBSD 0.3 August 30, 2007 MidnightBSD 0.3