request_key - Request a key from the kernel’s key management facility
key_serial_t request_key(const char *type, const char *description,
const char *callout_info, key_serial_t keyring);
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 searched.
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 userspace service such as /sbin/request-key to generate
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.
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.
ENOKEY No matching key was found.
An expired key was found, but no replacement could be obtained.
A revoked key was found, but no replacement could be obtained.
The attempt to generate a new key was rejected.
ENOMEM Insufficient memory to create a key.
EINTR The request was interrupted by a signal.
EDQUOT The key quota for this user would be exceeded by creating this
key or linking it to the keyring.
EACCES The keyring wasn’t available for modification by the user.
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.
keyctl(1), add_key(2), keyctl(2), request-key(8)
This page is part of release 3.24 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/.