minix/lib/libc/sys/access.2
Ben Gras 2fe8fb192f Full switch to clang/ELF. Drop ack. Simplify.
There is important information about booting non-ack images in
docs/UPDATING. ack/aout-format images can't be built any more, and
booting clang/ELF-format ones is a little different. Updating to the
new boot monitor is recommended.

Changes in this commit:

	. drop boot monitor -> allowing dropping ack support
	. facility to copy ELF boot files to /boot so that old boot monitor
	  can still boot fairly easily, see UPDATING
	. no more ack-format libraries -> single-case libraries
	. some cleanup of OBJECT_FMT, COMPILER_TYPE, etc cases
	. drop several ack toolchain commands, but not all support
	  commands (e.g. aal is gone but acksize is not yet).
	. a few libc files moved to netbsd libc dir
	. new /bin/date as minix date used code in libc/
	. test compile fix
	. harmonize includes
	. /usr/lib is no longer special: without ack, /usr/lib plays no
	  kind of special bootstrapping role any more and bootstrapping
	  is done exclusively through packages, so releases depend even
	  less on the state of the machine making them now.
	. rename nbsd_lib* to lib*
	. reduce mtree
2012-02-14 14:52:02 +01:00

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Groff

.\" $NetBSD: access.2,v 1.26 2010/05/03 05:53:56 jruoho Exp $
.\"
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\"
.\" @(#)access.2 8.2 (Berkeley) 4/1/94
.\"
.Dd May 3, 2010
.Dt ACCESS 2
.Os
.Sh NAME
.Nm access
.Nd check access permissions of a file or pathname
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In unistd.h
.Ft int
.Fn access "const char *path" "int mode"
.Sh DESCRIPTION
The
.Fn access
function checks the accessibility of the
file named by
.Fa path
for the access permissions indicated by
.Fa mode .
The value of
.Fa mode
is the bitwise inclusive OR of the access permissions to be
checked
.Pf ( Dv R_OK
for read permission,
.Dv W_OK
for write permission and
.Dv X_OK
for execute/search permission) or the existence test,
.Dv F_OK .
All components of the pathname
.Fa path
are checked for access permissions (including
.Dv F_OK ) .
.Pp
The real user ID is used in place of the effective user ID
and the real group access list
(including the real group ID) are
used in place of the effective ID for verifying permission.
.Pp
If a process has super-user privileges and indicates success for
.Dv R_OK
or
.Dv W_OK ,
the file may not actually have read or write permission bits set.
If a process has super-user privileges and indicates success for
.Dv X_OK ,
at least one of the user, group, or other execute bits is set.
(However, the file may still not be executable.
See
.Xr execve 2 . )
.Sh RETURN VALUES
If
.Fa path
cannot be found or if any of the desired access modes would
not be granted, then a \-1 value is returned; otherwise
a 0 value is returned.
.Sh ERRORS
Access to the file is denied if:
.Bl -tag -width Er
.It Bq Er EACCES
Permission bits of the file mode do not permit the requested
access, or search permission is denied on a component of the
path prefix.
The owner of a file has permission checked with respect to the
.Dq owner
read, write, and execute mode bits, members of the file's group
other than the owner have permission checked with respect to the
.Dq group
mode bits, and all others have permissions checked with respect to
the
.Dq other
mode bits.
.It Bq Er EFAULT
.Fa path
points outside the process's allocated address space.
.It Bq Er EIO
An I/O error occurred while reading from or writing to the file system.
.It Bq Er ELOOP
Too many symbolic links were encountered in translating the pathname.
.It Bq Er ENAMETOOLONG
A component of a pathname exceeded
.Brq Dv NAME_MAX
characters, or an entire path name exceeded
.Brq Dv PATH_MAX
characters.
.It Bq Er ENOENT
The named file does not exist.
.It Bq Er ENOTDIR
A component of the path prefix is not a directory.
.It Bq Er EROFS
Write access is requested for a file on a read-only file system.
.It Bq Er ETXTBSY
Write access is requested for a pure procedure (shared text)
file presently being executed.
.El
.Sh SEE ALSO
.Xr chmod 2 ,
.Xr execve 2 ,
.Xr stat 2 ,
.Xr secure_path 3
.Sh STANDARDS
The
.Fn access
function conforms to
.St -p1003.1-90 .
.Sh SECURITY CONSIDERATIONS
The
.Fn access
system call is a potential security hole due to race conditions.
It should never be used.
Set-user-ID and set-group-ID applications should restore the
effective user or group ID, and perform actions directly rather than use
.Fn access
to simulate access checks for the real user or group ID.
.Pp
The
.Fn access
system call may however have some value in providing clues to users as to
whether certain operations make sense for a particular filesystem object.
Arguably it also allows a cheaper file existence test than
.Xr stat 2 .