---
name: "VOP_ACCESS"
section: "9"
platform: "linux"
package: "freebsd-manpages"
version: "6.0-5"
release: "Debian 4.0 (Etch)"
platforms: ["linux", "freebsd"]
url: "https://new.carta.tech/VOP_ACCESS"
---

# VOP\_ACCESS(9)

check access permissions of a file or Unix domain socket

## NAME

**VOP\_ACCESS** – check access permissions of a file or Unix domain socket

## SYNOPSIS

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

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

*int*\

**VOP\_ACCESS**(*struct vnode \*vp*, *int mode*, *struct ucred \*cred*, *struct thread \*td*);

## DESCRIPTION

This entry point checks the access permissions of the file against the given credentials.

Its arguments are:

- *vp*

  The vnode of the file to check.

- *mode*

  The type of access required.

- *cred*

  The user credentials to check.

- *td*

  The thread which is checking.

The *mode* is a mask which can contain VREAD, VWRITE or VEXEC.

## LOCKS

The vnode will be locked on entry and should remain locked on return.

## RETURN VALUES

If the file is accessible in the specified way, then zero is returned, otherwise an appropriate error code is returned.

## PSEUDOCODE

```
int
vop_access(struct vnode *vp, int mode, struct ucred *cred, struct thread *td)
{
    int error;
    /*
     * Disallow write attempts on read-only file systems;
     * unless the file is a socket, fifo, or a block or
     * character device resident on the filesystem.
     */
    if (mode & VWRITE) {
	switch (vp->v_type) {
	case VDIR:
	case VLNK:
	case VREG:
	    if (vp->v_mount->mnt_flag & MNT_RDONLY)
		return EROFS;
	    break;
	}
    }
    /* If immutable bit set, nobody gets to write it. */
    if ((mode & VWRITE) && vp has immutable bit set)
	return EPERM;
    /* Otherwise, user id 0 always gets access. */
    if (cred->cr_uid == 0)
	return 0;
    mask = 0;
    /* Otherwise, check the owner. */
    if (cred->cr_uid == owner of vp) {
	if (mode & VEXEC)
	    mask |= S_IXUSR;
	if (mode & VREAD)
	    mask |= S_IRUSR;
	if (mode & VWRITE)
	    mask |= S_IWUSR;
	return (((mode of vp) & mask) == mask ? 0 : EACCES);
    }
    /* Otherwise, check the groups. */
    for (i = 0, gp = cred->cr_groups; i < cred->cr_ngroups; i++, gp++)
	if (group of vp == *gp) {
	    if (mode & VEXEC)
		mask |= S_IXGRP;
	    if (mode & VREAD)
		mask |= S_IRGRP;
	    if (mode & VWRITE)
		mask |= S_IWGRP;
	    return (((mode of vp) & mask) == mask ? 0 : EACCES);
	}
    /* Otherwise, check everyone else. */
    if (mode & VEXEC)
	mask |= S_IXOTH;
    if (mode & VREAD)
	mask |= S_IROTH;
    if (mode & VWRITE)
	mask |= S_IWOTH;
    return (((mode of vp) & mask) == mask ? 0 : EACCES);
}
```

## ERRORS

- \[EPERM\]

  An attempt was made to change an immutable file.

- \[EACCES\]

  The permission bits the file mode or the ACL do not permit the requested access.

## SEE ALSO

[vaccess(9)](/vaccess/9.md), [vaccess\_acl\_posix1e(9)](/vaccess_acl_posix1e/9.md), [vnode(9)](/vnode/9.md)

## AUTHORS

This manual page was written by Doug Rabson.