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KEYCTL_READ(2const) — Linux manual page

NAME \|LIBRARY \|SYNOPSIS \|DESCRIPTION \|RETURN VALUE \|ERRORS \|VERSIONS \|STANDARDS \|HISTORY \|SEE ALSO \|COLOPHON

KEYCTL_READ(2const)KEYCTL_READ(2const)

NAME top

       KEYCTL_READ - read a key

LIBRARY top

       Standard C library (libc,-lc)

SYNOPSIS top

#include <linux/keyctl.h>/* Definition ofKEY*constants */#include <sys/syscall.h>/* Definition ofSYS_*constants */#include <unistd.h>long syscall(size_t size;SYS_keyctl, KEYCTL_READ, key_serial_tkey,charbuf[_Nullablesize], size_tsize);

DESCRIPTION top

       Read the payload data of a key.       The ID of the key whose payload is to be read is specified inkey.       This can be the ID of an existing key, or any of the special key       IDs listed forKEYCTL_GET_KEYRING_ID(2const).       The payload is placed in the buffer pointed bybuf; the size of       that buffer must be specified insize.       The returned data will be processed for presentation according to       the key type.  For example, a keyring will return an array ofkey_serial_t entries representing the IDs of all the keys that are       linked to it.  Theuser key type will return its data as is.       Ifbuf is not NULL, as much of the payload data as will fit is       copied into the buffer.  On a successful return, the return value       is always the total size of the payload data.  To determine       whether the buffer was of sufficient size, check to see that the       return value is less than or equal to the value supplied insize.       The key must either grant the callerread permission, or grant the       callersearch permission when searched for from the process       keyrings (i.e., the key is possessed).

RETURN VALUE top

       On success, the amount of data that is available in the key,       irrespective of the provided buffer size.       On error, -1 is returned, anderrno is set to indicate the error.

ERRORS top

EOPNOTSUPP              The key type does not support reading (e.g., the type is"login").

VERSIONS top

       A wrapper is provided in thelibkeyutils library:keyctl_read(3).

STANDARDS top

       Linux.

HISTORY top

       Linux 2.6.10.

COLOPHON top

       This page is part of theman-pages (Linux kernel and C library       user-space interface documentation) project.  Information about       the project can be found at        ⟨https://www.kernel.org/doc/man-pages/⟩.  If you have a bug report       for this manual page, see       ⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.       This page was obtained from the tarball man-pages-6.15.tar.gz       fetched from       ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on       2025-08-11.  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 isnot       part of the original manual page), send a mail to       man-pages@man7.orgLinux man-pages 6.15            2025-06-28KEYCTL_READ(2const)

Pages that refer to this page:keyctl(2), KEYCTL_ASSUME_AUTHORITY(2const), KEYCTL_SETPERM(2const)

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