Managing File Systems
A file system is a structure of files and directories used to organize and store files on disks and other storage media. All disk-based computer systems have a file system. In Unix, file systems have two basic components: files and directories. A file is the actual information as it is stored on the disk, and a directory is a listing of the filenames. In addition to keeping track of filenames, the file system must also keep track of files' access dates, permissions, and ownership.
A hard disk consists of several separate disk platters mounted on a common spindle. Data stored on each platter surface is written and read by disk heads. The circular path a disk head traces over a spinning disk platter is called a track.
Each track is made up of a number of sectors laid end to end. A sector consists of a header, a trailer, and 512 bytes of data. The header and trailer contain error-checking information to help ensure the accuracy of the data. Taken together, the set of tracks traced across all of the individual disk platter surfaces for a single position of the heads is called a cylinder.
Devices and Drivers
In Solaris, each disk device is described in three ways, using three distinct naming conventions:
The system commands used to provide information about physical devices are described in Table 1.
You can add new devices to a system without requiring a reboot if your system supports hot-plug devices. It's all handled by the devfsadmd daemon that transparently builds the necessary configuration entries. Older commands such as drvconfig, disks, tapes, ports, and devlinks have been replaced by the devfsadm utility. The devfsadm command should now be used in place of all these commands; however, devfsadmd, the devfsadm daemon, automatically detects device configuration changes, so there should be no need to run this command interactively.
During the process of building the /devices directory, the devfsadmd daemon assigns each device a major device number by using the name-to-number mappings held in the /etc/name_to_major file. This file is maintained by the system. The major device number indicates the general device class, such as disk, tape, or serial line. The minor device number indicates the specific member within that class.
The instance name represents the kernel's abbreviated name for every possible device on the system. For example, on an Ultra system, dad0 represents the instance name of the IDE disk drive, and hme0 is the instance name for the network interface. Instance names are mapped to a physical device name in the /etc/path_to_inst file.
Virtual file systems, previously called pseudo file systems, are virtual or memory-based file systems that create duplicate paths to other disk-based file systems or provide access to special kernel information and facilities. Most virtual file systems do not use file system disk space, although a few exceptions exist. The following is a list of some of the more common types of virtual file systems:
Disks are divided into regions called disk slices or disk partitions using the format utility or the Solaris Management Console. Make sure you understand all of the Format menu options and what tasks they perform. The following displays the main menu options in the format utility:
disk - select a disk type - select (define) a disk type partition - select (define) a partition table current - describe the current disk format - format and analyze the disk repair - repair a defective sector label - write label to the disk analyze - surface analysis defect - defect list management backup - search for backup labels verify - read and display labels save - save new disk/partition definitions inquiry - show vendor, product and revision volname - set 8-character volume name !<cmd> - execute <cmd>, then return quit - Quit the format utility
PARTITION MENU: 0 - change '0' partition 1 - change '1' partition 2 - change '2' partition 3 - change '3' partition 4 - change '4' partition 5 - change '5' partition 6 - change '6' partition 7 - change '7' partition select - select a predefined table modify - modify a predefined partition table name - name the current table print - display the current table label - write partition map and label to the disk !<cmd> - execute <cmd>, then return quit - Quit the format utility
When you create a UFS, the disk slice is divided into cylinder groups. Disk configuration information is stored in the disk label. If you know the disk and slice number, you can display information for a disk by using the print volume table of contents (prtvtoc) command.
The slice is then divided into blocks to control and organize the structure of the files within the cylinder group. A UFS has the following four types of blocks. Each performs a specific function in the file system:
File systems can be mounted from the command line by using the mount command. The commands in Table 2 are used from the command line to mount and unmount file systems.
Common options used when mounting file systems are listed in Table 3.
Use the df command and its options to see the capacity of each file system mounted on a system, the amount of space available, and the percentage of space already in use. Use the du (directory usage) command to report the number of free disk blocks and files.
Creating a UFS
mkfs constructs a file system on the character (or raw) device found in the /dev/rdsk directory. Again, it is highly recommended that you do not run the mkfs command directly, but instead use the friendlier newfs command, which automatically determines all the necessary parameters required by mkfs to construct the file system.
The /etc/vfstab (virtual file system table) file contains a list of file systems to be automatically mounted when the system is booted to the multi-user state. Each column of information follows this format:
Use the fsck command to repair file systems. fsck is a multipass file system check program that performs successive passes over each file system, checking blocks and sizes, pathnames, connectivity, reference counts, and the map of free blocks (possibly rebuilding it). fsck also performs file system cleanup.
Volume management, with the vold daemon, is the mechanism that automatically mounts CD-ROMs and file systems when removable media containing recognizable file systems are inserted into the devices. The vold daemon is the workhorse behind volume manager. It is automatically started by the /etc/init.d/volmgt script. vold reads the /etc/vold.conf configuration file at startup. The vold.conf file contains the volume manager configuration information that vold uses.
Several other commands help you administer the volume manager on your system. They are described in Table 4.
File systems are checked and repaired with the fsck (file system check) command. fsck is a multipass file system check program that performs successive passes over each file system, checking blocks and sizes, pathnames, connectivity, reference counts, and the map of free blocks (possibly rebuilding it). fsck also performs cleanup.