man pages section 7: Device and Network Interfaces

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Updated: July 2014



pcfs - FAT formatted file system


#include <sys/param.h>
#include <sys/mount.h>
#include <sys/fs/pc_fs.h>

int mount(const char *spec, const char * dir, int  mflag,
     "pcfs", NULL, 0, char *optptr, int optlen);


pcfs is a file system type that enables direct access to files on FAT formatted disks from within the SunOS operating system.

Once mounted, pcfs provides standard SunOS file operations and semantics. Using pcfs, you can create, delete, read, and write files on a FAT formatted disk. You can also create and delete directories and list files in a directory.

pcfs supports FAT12 (floppies) and FAT16 and FAT32 file systems.

pcfs file systems can be force umounted using the –f argument to umount(1M).

The pcfs file system contained on the block special file identified by spec is mounted on the directory identified by dir. spec and dir are pointers to pathnames. mflag specifies the mount options. The MS_DATA bit in mflag must be set. Mount options can be passed to pcfs using the optptr and optlen arguments. See mount_pcfs(1M) for a list of mount options supported by pcfs.

Because FAT formatted media can record file timestamps between January 1st 1980 and December 31st 2127, it's not possible to fully represent UNIX time_t in pcfs for 32 bit or 64 bit programs. In particular, if post-2038 timestamps are present on a FAT formatted medium and pcfs returns these, 32bit applications may unexpectedly fail with EOVERFLOW errors. To prevent this, the default behaviour of pcfs has been modified to clamp post-2038 timestamps to the latest possible value for a 32bit time_t, which is January 19th 2038, 03:14:06 UTC when setting and retrieving file timestamps. You can override this behavior using the noclamptime mount option, as described in mount_pcfs(1M).

Timestamps on FAT formatted media are recorded in local time. If the recording and receiving systems use different timezones, the representation of timestamps shown on the two systems for the same medium might vary. To correct this, pcfs provides a timezone mount option to force interpretation of timestamps as read from a FAT formatted medium in a given timezone (that of the recorder). By default, the local timezone of the receiver is used. See mount_pcfs(1M) for details.

The root directory of a FAT formatted medium has no timestamps and pcfs returns the time when the mount was done as timestamp for the root of the filesystem.

The FAT filesystem doesn't support multiple links. As a result, the link count for all files and directories in pcfs is hard-coded as 1.

Mounting File Systems

You can use:

mount directory-name

if the following line is in your /etc/vfstab file:

device-special - directory-namepcfs − no rw

Use the following command to mount pcfs:

mount –F pcfs device-special:logical-drive directory-name

You can use:

mount directory-name

if the following line is in your /etc/vfstab file:

device-special:logical_drive  directory-name pcfs − no rw

device-special specifies the special block device file for the entire hard disk (/dev/dsk/cNtNdNp0 for a SCSI disk, and /dev/dsk/cNd Np0 for IDE disks) or the PCMCIA pseudo-floppy memory card (/dev/dsk/cNtNdNsN).

logical-drive specifies either the DOS logical drive letter (c through z) or a drive number (1 through 24). Drive letter c is equivalent to drive number 1 and represents the Primary DOS partition on the disk; drive letters d through z are equivalent to drive numbers 2 through 24, and represent DOS drives within the Extended FAT partition. Note that device-special and logical-drive must be separated by a colon.

directory-name specifies the location where the file system is mounted.

For example, to mount the Primary DOS partition from a SCSI hard disk, use:

mount –F pcfs /dev/dsk/cNtNdNp0:c /pcfs/c

To mount the first logical drive in the Extended DOS partition from an IDE hard disk, use:

mount –F pcfs /dev/dsk/cNdNp0:d /pcfs/d

To mount a PCMCIA pseudo-floppy memory card, with Volume Management not running (or not managing the PCMCIA media), use:

mount –F pcfs /dev/dsk/cNtNdNsN /pcfs


Files and directories created through pcfs must comply with either the FAT short file name convention or the long file name convention introduced with Windows 95. The FAT short file name convention is of the form filename[. ext], where filename generally consists of from one to eight upper-case characters, while the optional ext consists of from one to three upper-case characters.

The long file name convention is much closer to Solaris file names. A long file name can consist of any characters valid in a short file name, lowercase letters, non-leading spaces, the characters +,;=[], any number of periods, and can be up to 255 characters long. Long file names have an associated short file name for systems that do not support long file names (including earlier releases of Solaris). The short file name is not visible if the system recognizes long file names. pcfs generates a unique short name automatically when creating a long file name.

Given a long file name such as This is a really long filename.TXT, the short file name will generally be of the form THISIS~N.TXT, where N is a number. The long file name will probably get the short name THISIS~1.TXT, or THISIS~2.TXT if THISIS~1.TXT already exits (or THISIS~3.TXT if both exist, and so forth). If you use pcfs file systems on systems that do not support long file names, you may want to continue following the short file name conventions. See EXAMPLES.

When creating a file name, pcfs creates a short file name if it fits the FAT short file name format, otherwise it creates a long file name. This is because long file names take more directory space. Because the root directory of a pcfs file system is fixed size, long file names in the root directory should be avoided if possible.

When displaying file names, pcfs shows them exactly as they are on the media. This means that short names are displayed as uppercase and long file names retain their case. Earlier versions of pcfs folded all names to lowercase, which can be forced with the PCFS_MNT_FOLDCASE mount option. All file name searches within pcfs, however, are treated as if they were uppercase, so readme.txt and ReAdMe.TxT refer to the same file.

To format a PCMCIA pseudo-floppy memory card in FAT format in the SunOS system, use the DOS FORMAT command.

Boot Partitions

On x86 systems, hard drives may contain an fdisk partition reserved for the Solaris boot utilities. These partitions are special instances of pcfs. You can mount an x86 boot partition with the command:

mount –F pcfs device-special:boot directory-name

or you can use:

mount directory-name

if the following line is in your /etc/vfstab file:

device-special:boot − directory-name pcfs − no rw

device-special specifies the special block device file for the entire hard disk (/dev/dsk/cNtNdNp0)

directory-name specifies the location where the file system is mounted.

All files on a boot partition are owned by super-user. Only the super-user may create, delete, or modify files on a boot partition.


Example 1 Sample Displays of File Names

If you copy a file from a UNIX file system to pcfs, it displays as in pcfs, but may show up as FINANC~1.DAT in systems that do not support long file names.

The following are legal long file names. They are also illegal short file names:

Other systems that do not support long file names may see:


The short file name is generated from the initial characters of the long file name, so differentiate names in the first few characters. For example, these names:


result in these short names, which are not distinguishable:


These names, however:


result in the more descriptive short names:




pcfs mount command


32-bit kernel module

Environment Variables

See environ(5) for descriptions of the following environment variables for the current locale setting: LANG, LC_ALL, LC_CTYPE, and LC_COLLATE.

See also

chgrp(1), chown(1), dos2unix(1), eject(1), unix2dos(1), volcheck(1), mount(1M), mount_pcfs(1M), umount(1M), ctime(3C), vfstab(4), environ(5),


When mounting pcfs on a hard disk, make sure the first block on that device contains a valid fdisk partition table.

pcfs has a special provision for setting owner-ID, group-ID, or access permission on contents of the file system for the duration that a file system is mounted. See mount_pcfs (1M) for more information.


Only the following characters are allowed in pcfs short file names and extensions:


SunOS and FAT use different character sets and have different requirements for the text file format. Use the dos2unix(1) and unix2dos(1) commands to convert files between them.

pcfs offers a convenient transportation vehicle for files between Sun workstations and PCs. Because the FAT disk format was designed for use under DOS, it does not operate efficiently under the SunOS system and should not be used as the format for a regular local storage. Instead, use ufs for local storage within the SunOS system.

Although long file names can contain spaces (just as in UNIX file names), some utilities may be confused by them.

This implementation of pcfs conforms to the behavior exhibited by Windows 95 version 4.00.950.

When pcfs encounters long file names with non-ASCII characters, it converts such long file names in Unicode scalar values into UTF-8 encoded filenames so that they are legible and usable with any of Solaris UTF-8 locales. In the same context, when new file names with non-ASCII characters are created, pcfs expects that such file names are in UTF-8. This feature increases the interoperability of pcfs on Solaris with other operating systems.


pcfs should handle the disk change condition in the same way that DOS does, so you do not need to unmount the file system to change floppies.