---
name: "cap_set_file"
section: "3"
platform: "linux"
package: "libcap"
version: "2.78-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/cap_get_file"
---

# cap\_set\_file(3)

capability manipulation on files

Part of [cap\_get\_file(3)](/cap_get_file/3.md).

## NAME

cap\_get\_file, cap\_set\_file, cap\_get\_fd, cap\_set\_fd, cap\_get\_nsowner, cap\_set\_nsowner - capability manipulation on files

## SYNOPSIS

```
#include <sys/capability.h>
cap_t cap_get_file(const char *path_p);
int cap_set_file(const char *path_p, cap_t cap_p);
cap_t cap_get_fd(int fd);
int cap_set_fd(int fd, cap_t caps);
uid_t cap_get_nsowner(cap_t caps);
int cap_set_nsowner(cap_t caps, uid_t rootuid);
```

Link with *-lcap*.

## DESCRIPTION

**cap\_get\_file**() and **cap\_get\_fd**() allocate a capability state in working storage and set it to represent the capability state of the pathname pointed to by *path\_p* or the file open on descriptor *fd*. These functions return a pointer to the newly created capability state.  The effects of reading the capability state from any file other than a regular file is undefined.  The caller should free any releasable memory, when the capability state in working storage is no longer required, by calling **cap\_free**() with the used *cap\_t* as an argument.

**cap\_set\_file**() and **cap\_set\_fd**() set the values for all capability flags for all capabilities for the pathname pointed to by *path\_p* or the file open on descriptor *fd*, with the capability state identified by *cap\_p*. The new capability state of the file is completely determined by the contents of *cap\_p*. A NULL value for *cap\_p* is used to indicate that capabilities for the file should be deleted. For these functions to succeed, the calling process must have the **CAP\_SETFCAP** capability in its effective set and either the effective user ID of the process must match the file owner or the calling process must have the **CAP\_FOWNER** capability in its effective capability set.  The effects of writing the capability state to any file type other than a regular file are undefined.

A capability set held in memory can be associated with the root user ID in use in a specific user namespace. It is possible to get and set this value (in the memory copy) with **cap\_get\_nsowner**() and **cap\_set\_nsowner**() respectively. The root user ID is ignored by the libcap library in all cases other than when the capability is written to a file. Only if the value is non-zero will the library attempt to include it in the written file capability set.

## RETURN VALUE

**cap\_get\_file**() and **cap\_get\_fd**() return a non-NULL value on success, and NULL on failure.

**cap\_set\_file**() and **cap\_set\_fd**() return zero on success, and -1 on failure.

On failure, *errno* is set to **EACCES**, **EBADFD**, **ENAMETOOLONG**, **ENOENT**, **ENOMEM**, **ENOTDIR**, **EPERM**, or **EROFS**.

## CONFORMING TO

These functions are specified by withdrawn POSIX.1e draft specification.

## NOTES

Support for file capabilities is provided on Linux since version 2.6.24.

On Linux, the file Effective set is a single bit. If it is enabled, then all Permitted capabilities are enabled in the Effective set of the calling process when the file is executed; otherwise, no capabilities are enabled in the process's Effective set following an [**execve**(2)](/execve/2.md). Because the file Effective set is a single bit, if any capability is enabled in the Effective set of the *cap\_t* given to **cap\_set\_file**() or **cap\_set\_fd**(), then all capabilities whose Permitted or Inheritable flag is enabled must also have the Effective flag enabled. Conversely, if the Effective bit is enabled on a file, then the *cap\_t* returned by **cap\_get\_file()** and **cap\_get\_fd()** will have the Effective flag enabled for each capability that has the Permitted or Inheritable flag enabled.

## SEE ALSO

[**libcap**(3)](/libcap/3.md), [**cap\_clear**(3)](/cap_clear/3.md), [**cap\_copy\_ext**(3)](/cap_copy_ext/3.md), [**cap\_from\_text**(3)](/cap_from_text/3.md), [**cap\_get\_proc**(3)](/cap_get_proc/3.md), [**cap\_init**(3)](/cap_init/3.md), [**capabilities**(7)](/capabilities/7.md), [**user\_namespaces**(7)](/user_namespaces/7.md)