---
name: "KEYCTL_READ"
section: "2const"
platform: "linux"
package: "man-pages"
version: "6.19-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/KEYCTL_READ"
---

# KEYCTL\_READ(2const)

read a key

## NAME

KEYCTL\_READ - read a key

## LIBRARY

Standard C library (*libc*, *-lc*)

## SYNOPSIS

```
#include <linux/keyctl.h>  /* Definition of KEY* constants */
#include <sys/syscall.h>   /* Definition of SYS_* constants */
#include <unistd.h>
```

**long syscall(**size\_t size;              **SYS\_keyctl, KEYCTL\_READ, key\_serial\_t** *key***,**              **char** *buf***\[\_Nullable** *size***\], size\_t** *size***);**

## DESCRIPTION

Read the payload data of a key.

The ID of the key whose payload is to be read is specified in *key*. This can be the ID of an existing key, or any of the special key IDs listed for [**KEYCTL\_GET\_KEYRING\_ID**(2const)](/KEYCTL_GET_KEYRING_ID/2const.md).

The payload is placed in the buffer pointed by *buf*; the size of that buffer must be specified in *size*.

The returned data will be processed for presentation according to the key type. For example, a keyring will return an array of *key\_serial\_t* entries representing the IDs of all the keys that are linked to it. The *user* key type will return its data as is.

If *buf* 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 in *size*.

The key must either grant the caller *read* permission, or grant the caller *search* permission when searched for from the process keyrings (i.e., the key is possessed).

## RETURN VALUE

On success, the amount of data that is available in the key, irrespective of the provided buffer size.

On error, -1 is returned, and *errno* is set to indicate the error.

## ERRORS

- **EOPNOTSUPP**

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

## VERSIONS

A wrapper is provided in the *libkeyutils* library: [**keyctl\_read**(3)](/keyctl_read/3.md).

## STANDARDS

Linux.

## HISTORY

Linux 2.6.10.

## SEE ALSO

[**keyctl**(2)](/keyctl/2.md), [**keyctl\_read**(3)](/keyctl_read/3.md), [**keyctl\_read\_alloc**(3)](/keyctl_read_alloc/3.md)