config root man

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.\"	@(#)pathconf.2	8.1 (Berkeley) 6/4/93
.\" $FreeBSD: release/9.1.0/lib/libc/sys/pathconf.2 237216 2012-06-18 04:55:07Z eadler $
.\"
.Dd July 7, 2009
.Dt PATHCONF 2
.Os
.Sh NAME
.Nm pathconf ,
.Nm lpathconf ,
.Nm fpathconf
.Nd get configurable pathname variables
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In unistd.h
.Ft long
.Fn pathconf "const char *path" "int name"
.Ft long
.Fn lpathconf "const char *path" "int name"
.Ft long
.Fn fpathconf "int fd" "int name"
.Sh DESCRIPTION
The
.Fn pathconf ,
.Fn lpathconf
and
.Fn fpathconf
system calls provide a method for applications to determine the current
value of a configurable system limit or option variable associated
with a pathname or file descriptor.
.Pp
For
.Fn pathconf
and
.Fn lpathconf ,
the
.Fa path
argument is the name of a file or directory.
For
.Fn fpathconf ,
the
.Fa fd
argument is an open file descriptor.
The
.Fa name
argument specifies the system variable to be queried.
Symbolic constants for each name value are found in the include file
.Li <unistd.h> .
.Pp
The
.Fn lpathconf
system call is like
.Fn pathconf
except in the case where the named file is a symbolic link,
in which case
.Fn lpathconf
returns information about the link,
while
.Fn pathconf
returns information about the file the link references.
.Pp
The available values are as follows:
.Pp
.Bl -tag -width 6n
.It Li _PC_LINK_MAX
The maximum file link count.
.It Li _PC_MAX_CANON
The maximum number of bytes in terminal canonical input line.
.It Li _PC_MAX_INPUT
The minimum maximum number of bytes for which space is available in
a terminal input queue.
.It Li _PC_NAME_MAX
The maximum number of bytes in a file name.
.It Li _PC_PATH_MAX
The maximum number of bytes in a pathname.
.It Li _PC_PIPE_BUF
The maximum number of bytes which will be written atomically to a pipe.
.It Li _PC_CHOWN_RESTRICTED
Return 1 if appropriate privilege is required for the
.Xr chown 2
system call, otherwise 0.
.St -p1003.1-2001
requires appropriate privilege in all cases, but this behavior was optional
in prior editions of the standard.
.It Li _PC_NO_TRUNC
Return greater than zero if attempts to use pathname components longer than
.Brq Dv NAME_MAX
will result in an
.Bq Er ENAMETOOLONG
error; otherwise, such components will be truncated to
.Brq Dv NAME_MAX .
.St -p1003.1-2001
requires the error in all cases, but this behavior was optional in prior
editions of the standard, and some
.No non- Ns Tn POSIX Ns -compliant
file systems do not support this behavior.
.It Li _PC_VDISABLE
Returns the terminal character disabling value.
.It Li _PC_ASYNC_IO
Return 1 if asynchronous I/O is supported, otherwise 0.
.It Li _PC_PRIO_IO
Returns 1 if prioritised I/O is supported for this file,
otherwise 0.
.It Li _PC_SYNC_IO
Returns 1 if synchronised I/O is supported for this file, otherwise 0.
.It Li _PC_ALLOC_SIZE_MIN
Minimum number of bytes of storage allocated for any portion of a file.
.It Li _PC_FILESIZEBITS
Number of bits needed to represent the maximum file size.
.It Li _PC_REC_INCR_XFER_SIZE
Recommended increment for file transfer sizes between
.Dv _PC_REC_MIN_XFER_SIZE
and
.Dv _PC_REC_MAX_XFER_SIZE .
.It Li _PC_REC_MAX_XFER_SIZE
Maximum recommended file transfer size.
.It Li _PC_REC_MIN_XFER_SIZE
Minimum recommended file transfer size.
.It Li _PC_REC_XFER_ALIGN
Recommended file transfer buffer alignment.
.It Li _PC_SYMLINK_MAX
Maximum number of bytes in a symbolic link.
.It Li _PC_ACL_EXTENDED
Returns 1 if an Access Control List (ACL) can be set on the specified
file, otherwise 0.
.It Li _PC_ACL_NFS4
Returns 1 if an NFSv4 ACLs can be set on the specified
file, otherwise 0.
.It Li _PC_ACL_PATH_MAX
Maximum number of ACL entries per file.
.It Li _PC_CAP_PRESENT
Returns 1 if a capability state can be set on the specified file,
otherwise 0.
.It Li _PC_INF_PRESENT
Returns 1 if an information label can be set on the specified file,
otherwise 0.
.It Li _PC_MAC_PRESENT
Returns 1 if a Mandatory Access Control (MAC) label can be set on the
specified file, otherwise 0.
.It Li _PC_MIN_HOLE_SIZE
If a file system supports the reporting of holes (see
.Xr lseek 2 ) ,
.Fn pathconf
and
.Fn fpathconf
return a positive number that represents the minimum hole size returned in
bytes.
The offsets of holes returned will be aligned to this same value.
A special value of 1 is returned if the file system does not specify the minimum
hole size but still reports holes.
.El
.Sh RETURN VALUES
If the call to
.Fn pathconf
or
.Fn fpathconf
is not successful, \-1 is returned and
.Va errno
is set appropriately.
Otherwise, if the variable is associated with functionality that does
not have a limit in the system, \-1 is returned and
.Va errno
is not modified.
Otherwise, the current variable value is returned.
.Sh ERRORS
If any of the following conditions occur, the
.Fn pathconf
and
.Fn fpathconf
system calls shall return -1 and set
.Va errno
to the corresponding value.
.Bl -tag -width Er
.It Bq Er EINVAL
The value of the
.Fa name
argument is invalid.
.It Bq Er EINVAL
The implementation does not support an association of the variable
name with the associated file.
.El
.Pp
The
.Fn pathconf
system call
will fail if:
.Bl -tag -width Er
.It Bq Er ENOTDIR
A component of the path prefix is not a directory.
.It Bq Er ENAMETOOLONG
A component of a pathname exceeded
.Brq Dv NAME_MAX
characters (but see
.Dv _PC_NO_TRUNC
above),
or an entire path name exceeded
.Brq Dv PATH_MAX
characters.
.It Bq Er ENOENT
The named file does not exist.
.It Bq Er EACCES
Search permission is denied for a component of the path prefix.
.It Bq Er ELOOP
Too many symbolic links were encountered in translating the pathname.
.It Bq Er EIO
An I/O error occurred while reading from or writing to the file system.
.El
.Pp
The
.Fn fpathconf
system call
will fail if:
.Bl -tag -width Er
.It Bq Er EBADF
The
.Fa fd
argument
is not a valid open file descriptor.
.It Bq Er EIO
An I/O error occurred while reading from or writing to the file system.
.El
.Sh SEE ALSO
.Xr lseek 2 ,
.Xr sysctl 3
.Sh HISTORY
The
.Fn pathconf
and
.Fn fpathconf
system calls first appeared in
.Bx 4.4 .
The
.Fn lpathconf
system call first appeared in
.Fx 8.0 .