KEYCTL_READ(3)           Linux Key Management Calls           KEYCTL_READ(3)

NAME         top

       keyctl_read - read a key

SYNOPSIS         top

       #include <keyutils.h>

       long keyctl_read(key_serial_t key, char *buffer,

       long keyctl_read_alloc(key_serial_t key, void **_buffer);

DESCRIPTION         top

       keyctl_read() reads the payload of a key if the key type supports it.

       The caller must have read permission on a key to be able to read it.

       buffer and buflen specify the buffer into which the payload data will
       be placed.  If the buffer is too small, the full size of the payload
       will be returned and no copy will take place.

       keyctl_read_alloc() is similar to keyctl_read() except that it
       allocates a buffer big enough to hold the payload data and places the
       data in it.  If successful, a pointer to the buffer is placed in
       *_buffer.  The caller must free the buffer.

       keyctl_read_alloc() adds a NUL character after the data it retrieves,
       though this is not counted in the size value it returns.


       This call can be used to list the contents of a keyring.  The data is
       presented to the user as an array of key_serial_t values, each of
       which corresponds to a key to which the keyring holds a link.

       The size of the keyring will be sizeof(key_serial_t) multiplied by
       the number of keys.  The size of key_serial_t is invariant across
       different word sizes, though the byte-ordering is as appropriate for
       the kernel.

RETURN VALUE         top

       On success keyctl_read() returns the amount of data placed into the
       buffer.  If the buffer was too small, then the size of buffer
       required will be returned, but no data will be transferred.

       On success keyctl_read_alloc() returns the amount of data in the

       On error, both functions set errno to an appropriate code and return
       the value -1.

ERRORS         top

       ENOKEY The key specified is invalid.

              The key specified has expired.

              The key specified had been revoked.

       EACCES The key exists, but is not readable by the calling process.

              The key type does not support reading of the payload data.

LINKING         top

       This is a library function that can be found in libkeyutils.  When
       linking, -lkeyutils should be specified to the linker.

SEE ALSO         top

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

COLOPHON         top

       This page is part of the keyutils (key management utilities) project.
       Information about the project can be found at [unknown -- if you
       know, please contact] If you have a bug report for
       this manual page, send it to  This page was
       obtained from the project's upstream Git repository 
       on 2017-03-13.  If you discover any rendering problems in this HTML
       version of the page, or you believe there is a better or more up-to-
       date source for the page, or you have corrections or improvements to
       the information in this COLOPHON (which is not part of the original
       manual page), send a mail to

Linux                            21 Feb 2014                  KEYCTL_READ(3)