---
name: "acl_set_file"
section: "3"
platform: "linux"
package: "acl"
version: "2.4.0-1"
release: "Arch Linux 2026-11-01"
platforms: ["linux", "freebsd"]
url: "https://new.carta.tech/acl_set_file"
---

# acl\_set\_file(3)

set an ACL by filename

## NAME

**acl\_set\_file**, **acl\_set\_file\_at** – set an ACL by filename

## LIBRARY

Linux Access Control Lists library (libacl, -lacl).

## SYNOPSIS

**#include \<sys/types.h\>**

**#include \<sys/acl.h\>**

*int*\

**acl\_set\_file**(*const char \*path\_p*, *acl\_type\_t type*, *acl\_t acl*);

*int*\

**acl\_set\_file\_at**(*int dirfd*, *const char \*path\_p*, *int at\_flags*, *acl\_type\_t type*, *acl\_t acl*);

## DESCRIPTION

The **acl\_set\_file**() function associates an access ACL with a file or directory, or associates a default ACL with a directory. The pathname for the file or directory is given in the argument *path\_p*. If *path\_p* is a symbolic link, **acl\_set\_file**() operates on the file or directory the link refers to.

The effective user ID of the process must match the owner of the file or directory or the process must have the CAP\_FOWNER capability for the request to succeed.

The value of the argument *type* is used to indicate whether the access ACL or the default ACL associated with *path\_p* is being set. If the *type* parameter is ACL\_TYPE\_ACCESS, the access ACL of *path\_p* shall be set. If the *type* parameter is ACL\_TYPE\_DEFAULT, the default ACL of *path\_p* shall be set. If the argument *type* specifies a type of ACL that cannot be associated with *path\_p*, then the function fails.

The *acl* parameter must reference a valid ACL according to the rules described on the [acl\_valid(3)](/acl_valid/3.md) manual page if the *type* parameter is ACL\_TYPE\_ACCESS, and must either reference a valid ACL or an ACL with zero ACL entries if the *type* parameter is ACL\_TYPE\_DEFAULT. If the *acl* parameter references an empty ACL, then the **acl\_set\_file**() function removes any default ACL associated with the directory referred to by the *path\_p* parameter.

### Fn acl\_set\_file\_at

The **acl\_set\_file\_at**() function operates in exactly the same way as **acl\_set\_file**(), except for the differences described here.

If the pathname given in *path\_p* is relative, then it is interpreted relative to the directory referred to by the file descriptor *dirfd* (rather than relative to the current working directory of the calling process, as is done by **acl\_set\_file**()).

If *path\_p* is relative and *dirfd* is the special value AT\_FDCWD, then *path\_p* is interpreted relative to the current working directory of the calling process (like **acl\_set\_file**()).

If *path\_p* is absolute, then *dirfd* is ignored.

The *at\_flags* argument can either be 0, or include one or more of the following flags ORed:

- AT\_EMPTY\_PATH

  If *path\_p* is an empty string, operate on the file referred to by *dirfd* (which may have been obtained using the [open(2)](/open/2.md) O\_PATH flag). In this case, *dirfd* can refer to any type of file, not just a directory, and the behavior of **acl\_set\_file\_at**() is similar to that of **acl\_set\_fd**().

- AT\_SYMLINK\_NOFOLLOW

  If *path\_p* refers to a symbolic link, do not dereference it: instead, fail the operation and set the global variable *errno* to ENOTSUP. This indicates that the symbolic link cannot have ACLs.

## RETURN VALUE

The **acl\_set\_file()** and **acl\_set\_file\_at()** functions return the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

## ERRORS

If any of the following conditions occur, the **acl\_set\_file**() and **acl\_set\_file\_at**() functions return -1 and set *errno* to the corresponding value:

- \[EACCES\]

  Search permission is denied for a component of the path prefix or the object exists and the process does not have appropriate access rights.

  Argument *type* specifies a type of ACL that cannot be associated with *path\_p*.

- \[EBADF\]

  The argument *path\_p* is relative but the argument *dirfd* is neither AT\_FDCWD nor a valid file descriptor.

- \[EINVAL\]

  The argument *acl* does not point to a valid ACL.

  The ACL has more entries than the file referred to by *path\_p* can obtain.

  The *type* parameter is not ACL\_TYPE\_ACCESS or ACL\_TYPE\_DEFAULT.

  The *type* parameter is ACL\_TYPE\_DEFAULT, but the file referred to by *path\_p* is not a directory.

  An invalid flag was specified in the *at\_flags* argument.

- \[ENAMETOOLONG\]

  The length of the argument *path\_p* is too long.

- \[ENOENT\]

  The named object does not exist or the argument *path\_p* points to an empty string.

- \[ENOSPC\]

  The directory or file system that would contain the new ACL cannot be extended or the file system is out of file allocation resources.

- \[ENOTDIR\]

  A component of the path prefix is not a directory.

  The argument *path\_p* is relative and the argument *dirfd* is a file descriptor referring to a file other than a directory.

- \[ENOTSUP\]

  The argument *at\_flags* includes the flag AT\_SYMLINK\_NOFOLLOW and *path\_p* is a symbolic link.

  The file identified by *path\_p* cannot be associated with the ACL because the file system on which the file is located does not support this.

- \[EPERM\]

  The process does not have appropriate privilege to perform the operation to set the ACL.

- \[EROFS\]

  This function requires modification of a file system which is currently read-only.

## STANDARDS

IEEE Std 1003.1e draft 17 (“POSIX.1e”, abandoned)

The behavior of **acl\_set\_file**() when the *acl* parameter refers to an empty ACL and the *type* parameter is ACL\_TYPE\_DEFAULT is an extension in the Linux implementation, in order that all values returned by **acl\_get\_file**() can be passed to **acl\_set\_file**(). The POSIX.1e function for removing a default ACL is **acl\_delete\_def\_file**().

Function **acl\_get\_file\_at**() is a Linux specific extension.

## SEE ALSO

[acl\_delete\_def\_file(3)](/acl_delete_def_file/3.md), [acl\_get\_file(3)](/acl_get_file/3.md), [acl\_set\_fd(3)](/acl_set_fd/3.md), [acl\_valid(3)](/acl_valid/3.md), [acl(5)](/acl/5.md)

## AUTHOR

Derived from the FreeBSD manual pages written by Robert N M Watson ⟨rwatson@FreeBSD.org⟩, and adapted for Linux by Andreas Gruenbacher ⟨andreas.gruenbacher@gmail.com⟩.