Mounting File Systems

Objective:

Explain how to perform mounts and unmounts.

File systems can be mounted from the command line by using the mount command. The commands in Table 1.15 are used from the command line to mount and unmount file systems.

Table 1.15. File System Commands

Command	Description
mount	Mounts specified file systems and remote resources
mountall	Mounts all file systems specified in a file system table (vfstab)
umount	Unmounts specified file systems and remote resources
umountall	Unmounts all file systems specified in a file system table

After you create a file system, you need to make it available. You make file systems available by mounting them. Using the mount command, you attach a file system to the system directory tree at the specified mount point, and it becomes available to the system. The root file system is mounted at boot time and cannot be unmounted. Any other file system can be mounted or unmounted from the root file system with few exceptions.

The syntax for mount is as follows:

mount -F <fstype> <options> [ -o <specific_options> ] <-O> device_to_mount mountpoint

Table 1.16 describes options to the mount command.

Table 1.16. The mount Command Options

Option	Description
-F <fstype>	Used to specify the file system type <fstype> on which to operate. If fstype is not specified, it must be determined from the /etc/vfstab file or by consulting /etc/default/fs or /etc/dfs/fstypes.
-g	Globally mount the file system. On a clustered system, this globally mounts the file system on all nodes of the cluster.
-m	Mounts the file system without making an entry in /etc/mnttab.
-r	Mounts the file system as read-only.
-O	Overlay mount. Allows the file system to be mounted over an existing mount point, making the underlying file system inaccessible. If a mount is attempted on a preexisting mount point without setting this flag, the mount fails, producing the error device busy.
-p	Prints the list of mounted file systems in the /etc/vfstab format. This must be the only option specified.
-v	Prints the list of mounted file systems in verbose format. This must be the only option specified.
-V	Echoes the complete command line but does not execute the command. umount generates a command line by using the options and arguments provided by the user and adding to them information derived from /etc/mnttab. This option should be used to verify and validate the command line.
-o	Specifies fstype-specific options. These are generic options that can be specified with the -o option. If you specify multiple options, separate them with commas (no spaces)for example, -o ro,nosuid. Additionally, file system specific options are described later in this chapter and in their respective man pages (such as man mount_ufs and man mount_nfs). devices | nodevicesAllow or disallow the opening of device-special files. The default is devices. exec | noexecAllow or disallow executing programs in the file system. rw|roSpecifies read/write or read-only. The default is read/write. nbmand | nonbmandAllow or disallow non-blocking mandatory locking semantics on this file system. Non-blocking mandatory locking is disallowed by default. nosuidDisallows setuid execution and prevents devices on the file system from being opened. The default is to enable setuid execution and to allow devices to be opened. remountWith rw, remounts a file system with read/write access. mMounts the file system without making an entry in /etc/mnttab. largefilesSpecifies that a file system might contain one or more files larger than 2GB. It is not required that a file system mounted with this option contain files larger than 2GB, but this option allows such files within the file system. largefiles is the default. nolargefilesProvides total compatibility with previous file system behavior, enforcing the 2GB maximum file size limit.

The following examples illustrate the options described in Table 1.16.

A file system has been created on disk c0t0d0 on slice s0. The directory to be mounted on this disk slice is /home2. To mount the file system, first create the directory called /home2 and then type the following:

mount /dev/dsk/c0t0d0s0 /home2

If the file system has been mounted, you return to a command prompt. No other message is displayed.

When the UFS file system is mounted with no options, a default set of file system specific options are usedthey are explained in Table 1.17. Options specific to the UFS file system are also described in the mount_ufs man pages.

Table 1.17. Mount Default Options for a UFS File System

Option	Description
read/write	Indicates that file system can be read and written to.
setuid	Permits the execution of setuid programs in the file system.
devices	Allow the opening of device-special files.
intr	Allows keyboard interrupts to kill a process that is waiting for an operation on a locked file system.
logging	Indicates that logging is enabled for the UFS file system. This is the default for the Solaris 10 OS.
largefiles	Allows for the creation of files larger than 2 Gbytes. A file system mounted with this option can contain files larger than 2 Gbytes.
xattr	Supports extended attributes not found in standard Unix file systems.
onerror=panic	Specifies the action that the UFS file system should take to recover from an internal inconsistency on a file system. An action can be specified as: panicCauses a forced system shutdown. This is the default. lockApplies a file system lock to the file system. umountForcibly unmounts the file system.

In the next example, the -v option is used with the mount command to display a list of all mounted file systems:

mount -v

The system responds with this:

# mount -v
/dev/dsk/c0t0d0s0 on / type ufs \
read/write/setuid/devices/intr/largefiles/logging/xattr/onerror=panic/dev=2200008 \
on Fri Aug  5 11:32:05 2005
/devices on /devices type devfs read/write/setuid/devices/dev=4380000 \
 on Fri Aug  5 11:31:47 2005 ctfs on /system/contract type ctfs \
read/write/setuid/devices/dev=43c0001 on Fri Aug  5 11:31:47 2005
proc on /proc type proc read/write/setuid/devices/dev=4400000 on\
 Fri Aug  5 11:31:47 2005
mnttab on /etc/mnttab type mntfs read/write/setuid/devices/dev=4440001 \
on Fri Aug  5 11:31:47 2005

swap on /etc/svc/volatile type tmpfs read/write/setuid/devices/xattr/dev=4480001 \
on Fri Aug  5 11:31:47 2005

objfs on /system/object type objfs read/write/setuid/devices/dev=44c0001 on \
Fri Aug  5 11:31:47 2005

/dev/dsk/c0t0d0s6 on /usr type ufs \
read/write/setuid/devices/intr/largefiles/logging/xattr/onerror=panic/dev=220000e \
on Fri Aug  5 11:32:06 2005
fd on /dev/fd type fd read/write/setuid/devices/dev=4640001 \
on Fri Aug  5 11:32:06 2005
/dev/dsk/c0t0d0s1 on /var type ufs \
read/write/setuid/devices/intr/largefiles/logging/xattr/onerror=panic/dev=2200009 \
on Fri Aug  5 11:32:09 2005
swap on /tmp type tmpfs read/write/setuid/devices/xattr/dev=4480002 \
on Fri Aug  5 11:32:09 2005
swap on /var/run type tmpfs read/write/setuid/devices/xattr/dev=4480003 \
on Fri Aug  5 11:32:09 2005
/dev/dsk/c0t0d0s4 on /data type ufs \
read/write/setuid/devices/intr/largefiles/logging/xattr/onerror=panic/dev=220000c \
on Fri Aug  5 11:32:16 2005
/dev/dsk/c0t0d0s5 on /opt type ufs \
read/write/setuid/devices/intr/largefiles/logging/xattr/onerror=panic/dev=220000d \
on Fri Aug  5 11:32:16 2005
/dev/dsk/c0t0d0s7 on /export/home type ufs \
read/write/setuid/devices/intr/largefiles/logging/xattr/onerror=panic/dev=220000f \
on Fri Aug  5 11:32:16 2005

The following example mounts a file system as read-only:

mount -o ro /dev/dsk/c0t0d0s0 /home2

The next example uses the mount command to mount a directory to a file system as read/writeable, disallow setuid execution, and allow the creation of large files:

mount -o rw,nosuid,largefiles /dev/dsk/c0t0d0s0 /home2

Type mount with no options to verify that the file system has been mounted and to review the mount options that were used:

mount

The system responds with information about all mounted file systems, including /home2:

/home2 on /dev/dsk/c0t0d0s0 read/write/nosuid/largefiles on\
 Tue Jul 16 06:56:33 2005

Mounting a File System with Large Files

On a Solaris system, a large file is a regular file whose size is greater than or equal to 2GB. A small file is a regular file whose size is less than 2GB. Some utilities can handle large files, and others cannot. A utility is called large fileaware if it can process large files in the same manner that it does small files. A large fileaware utility can handle large files as input and can generate large files as output. The newfs, mkfs, mount, umount, tunefs, labelit, and quota utilities are all large fileaware for UFS file systems.

On the other hand, a utility is called large filesafe if it causes no data loss or corruption when it encounters a large file. A utility that is large filesafe cannot properly process a large file, so it returns an appropriate error. Some examples of utilities that are not large fileaware but are large filesafe include the vi editor and the mailx and lp commands. A full list of commands that are large fileaware and large filesafe can be found in the online manual pages.

The largefiles mount option lets users mount a file system containing files larger than 2GB. The largefiles mount option is the default state for the Solaris 10 environment. The largefiles option means that a file system mounted with this option might contain one or more files larger than 2GB.

You must explicitly use the nolargefiles mount option to disable this behavior. The nolargefiles option provides total compatibility with previous file system behavior, enforcing the 2GB maximum file size limit.

Mounting a File System with UFS Logging Enabled

The UFS logging feature eliminates file system inconsistency, which can significantly reduce the time of system reboots. UFS logging is the default in Solaris 10 and does not need to be specified when mounting a file system. Use the nologging option in the /etc/vfstab file or as an option to the mount command to disable UFS logging on a file system.

UFS logging is the process of storing file system operations to a log before the transactions are applied to the file system. Because the file system can never become inconsistent, fsck can usually be bypassed, which reduces the time to reboot a system if it crashes or after an unclean halt.

The UFS log is allocated from free blocks on the file system. It is sized at approximately 1MB per 1GB of file system, up to a maximum of 64MB. The default is logging for all UFS file systems.