REQUEST_KEY(2)           Linux Key Management Calls           REQUEST_KEY(2)

NAME         top

       request_key - request a key from the kernel's key management facility

SYNOPSIS         top

       #include <keyutils.h>

       key_serial_t request_key(const char *type, const char *description,
                                const char *callout_info,
                                key_serial_t keyring);

DESCRIPTION         top

       request_key() asks the kernel to find a key of the given type that
       matches the specified description and, if successful, to attach it to
       the nominated keyring and to return its serial number.

       request_key() first recursively searches all the keyrings attached to
       the calling process in the order thread-specific keyring, process-
       specific keyring and then session keyring for a matching key.

       If request_key() is called from a program invoked by request_key() on
       behalf of some other process to generate a key, then the keyrings of
       that other process will be searched next, using that other process's
       UID, GID, groups, and security context to control access.

       The keys in each keyring searched are checked for a match before any
       child keyrings are recursed into.  Only keys that are searchable for
       the caller may be found, and only searchable keyrings may be

       If the key is not found, then, if callout_info is set, this function
       will attempt to look further afield.  In such a case, the
       callout_info is passed to a user-space service such as
       /sbin/request-key to generate the key.

       If that is unsuccessful also, then an error will be returned, and a
       temporary negative key will be installed in the nominated keyring.
       This will expire after a few seconds, but will cause subsequent calls
       to request_key() to fail until it does.

       The keyring serial number may be that of a valid keyring to which the
       caller has write permission, or it may be a special keyring ID:

              This specifies the caller's thread-specific keyring.

              This specifies the caller's process-specific keyring.

              This specifies the caller's session-specific keyring.

              This specifies the caller's UID-specific keyring.

              This specifies the caller's UID-session keyring.

       If a key is created, no matter whether it's a valid key or a negative
       key, it will displace any other key of the same type and description
       from the destination keyring.

RETURN VALUE         top

       On success request_key() returns the serial number of the key it
       found.  On error, the value -1 will be returned and errno will have
       been set to an appropriate error.

ERRORS         top

       EACCES The keyring wasn't available for modification by the user.

       EDQUOT The key quota for this user would be exceeded by creating this
              key or linking it to the keyring.

       EINTR  The request was interrupted by a signal; see signal(7).

              An expired key was found, but no replacement could be

              The attempt to generate a new key was rejected.

              A revoked key was found, but no replacement could be obtained.

       ENOKEY No matching key was found.

       ENOMEM Insufficient memory to create a key.

LINKING         top

       Although this is a Linux system call, it is not present in libc but
       can be found rather in libkeyutils.  When linking, -lkeyutils should
       be specified to the linker.

SEE ALSO         top

       keyctl(1), add_key(2), keyctl(2), keyctl(3), keyrings(7),

COLOPHON         top

       This page is part of release 4.08 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at

Linux                            2016-10-08                   REQUEST_KEY(2)