REQUEST_KEY(2) Linux Key Management Calls REQUEST_KEY(2)
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,
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
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 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 dis-
place 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.
EACCES The keyring wasn't available for modification by the user.
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
An expired key was found, but no replacement could be obtained.
The attempt to generate a new key was rejected.
A revoked key was found, but no replacement could be obtained.
ENOMEM Insufficient memory to create a key.
ENOKEY No matching key was found.
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)
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Linux 2010-02-25 REQUEST_KEY(2)