Exercise 19. Filesystems: mounting, mount, /etc/fstab
I hope you are familiar with concept of partitions. In case if you are not I will introduce you briefly to it. First, quote from Wikipedia:
Disk partitioning is the act of dividing a hard disk drive into multiple logical storage units referred to as partitions, to treat one physical disk drive as if it were multiple disks.
Take a look:
user1@vm1:~$ sudo parted /dev/vda GNU Parted 2.3 Using /dev/vda Welcome to GNU Parted! Type 'help' to view a list of commands. (parted) unit GB (parted) p Model: Virtio Block Device (virtblk) Disk /dev/vda: 17.2GB Sector size (logical/physical): 512B/512B Partition Table: msdos Number Start End Size Type File system Flags 1 0.00GB 13.3GB 13.3GB extended 5 0.00GB 1.02GB 1.02GB logical ext3 boot 6 1.03GB 2.05GB 1.02GB logical linux-swap(v1) 7 2.05GB 3.07GB 1.02GB logical ext3 8 3.07GB 5.12GB 2.05GB logical ext3 9 5.12GB 9.22GB 4.09GB logical ext3 10 9.22GB 13.3GB 4.09GB logical ext3 (parted)
This is one physical hard disk which is divided in 7 different partitions. The reasons to do do are numerous, but best understood as an application of “divide and conquer” principle. When divided in such a way one rogue program can not bring whole sever down by consuming all disk space, this program will be limited to its partition. I will not talk about partitioning disks just just yet, but I will continue taking about file systems, by quoting Wikipedia again:
A file system (or filesystem) is a means to organize data expected to be retained after a program terminates by providing procedures to store, retrieve and update data, as well as manage the available space on the device(s) which contain it. A file system organizes data in an efficient manner and is tuned to the specific characteristics of the device. A tight coupling usually exists between the operating system and the file system. Some file systems provide mechanisms to control access to the data and metadata. Ensuring reliability is a major responsibility of a file system. Some file systems allow multiple programs to update the same file at nearly the same time.
Unix-like operating systems create a virtual file system, which makes all the files on all the devices appear to exist in a single hierarchy. This means, in those systems, there is one root directory, and every file existing on the system is located under it somewhere. Unix-like systems can use a RAM disk or network shared resource as its root directory.
What this means is that all file systems are integrated in one big tree. For those familiar with Microsoft Windows this means that instead C:, D:, and so on naming scheme there is a single root, /, to which all other partitions connect. The process of connecting a file system to existing directory is called mounting. A directory to which a file system is connected is called a mount point. Again, take a look:
user1@vm1:~$ mount /dev/vda5 on / type ext3 (rw,errors=remount-ro) tmpfs on /lib/init/rw type tmpfs (rw,nosuid,mode=0755) proc on /proc type proc (rw,noexec,nosuid,nodev) sysfs on /sys type sysfs (rw,noexec,nosuid,nodev) udev on /dev type tmpfs (rw,mode=0755) tmpfs on /dev/shm type tmpfs (rw,nosuid,nodev) devpts on /dev/pts type devpts (rw,noexec,nosuid,gid=5,mode=620) /dev/vda10 on /home type ext3 (rw) /dev/vda7 on /tmp type ext3 (rw) /dev/vda9 on /usr type ext3 (rw) /dev/vda8 on /var type ext3 (rw)
This are the same partitions I showed you earlier in this list you their mount points. Ones which do not start with /dev/vda are virtual file systems, which allow to access different system facilities, but they are not relevant for this exercise. Now let us take a look at /etc/fstab file:
user1@vm1:~$ cat /etc/fstab # /etc/fstab: static file system information. # # Use 'blkid' to print the universally unique identifier for a # device; this may be used with UUID= as a more robust way to name devices # that works even if disks are added and removed. See fstab(5). # # <file system> <mount point> <type> <options> <dump> <pass> proc /proc proc defaults 0 0 # / was on /dev/vda5 during installation UUID=128559db-a2e0-4983-91ad-d4f43f27da49 / ext3 errors=remount-ro 0 1 # /home was on /dev/vda10 during installation UUID=32852d29-ddee-4a8d-9b1e-f46569a6b897 /home ext3 defaults 0 2 # /tmp was on /dev/vda7 during installation UUID=869db6b4-aea0-4a25-8bd2-f0b53dd7a88e /tmp ext3 defaults 0 2 # /usr was on /dev/vda9 during installation UUID=0221be16-496b-4277-b131-2371ce097b44 /usr ext3 defaults 0 2 # /var was on /dev/vda8 during installation UUID=2db00f94-3605-4229-8813-0ee23ad8634e /var ext3 defaults 0 2 # swap was on /dev/vda6 during installation UUID=3a936af2-2c04-466d-b98d-09eacc5d104c none swap sw 0 0 /dev/scd0 /media/cdrom0 udf,iso9660 user,noauto 0 0
Looks scary, but let us take one line:
# <file system> <mount point> <type> <options> <dump> <pass> UUID=128559db-a2e0-4983-91ad-d4f43f27da49 / ext3 errors=remount-ro 0 1
And take it apart field by field:
UUID=128559db-a2e0-4983-91ad-d4f43f27da49 # Filesystem to mount. This UUID is synonim for /dev/vda5 / # This is root filesystem, mount it to / ext3 # This is ext3 filesystem. There are many different filesystems out there errors=remount-ro # If any errors encountered during mounting filesystem should be remounted read-only 0 # This filesystem should not be backed up by dump utility 1 # This filesystem should be checked first by fsck utility
As always, this information is available to you via man fstab. Now I will show you several commands for working with existing file systems:
- mount — print out all mounted filesystems.
- mount -a — mount all filesystem described in /etc/fstab.
- mount /dev/sda<N> /<mount point> — mount a partition.
- umount /dev/sda<N> /<mount point> — mount a partition.
- mount -h — print out short help about using mount.
- fsck — check partition for errors.
- blkid — print out unique partition identifiers.
Now you will learn how to list mounted partitions, mount and unmount them.
Do this
1: cat /etc/fstab 2: mount 3: sudo blkid 4: sudo umount /tmp 5: mount 6: sudo fsck /tmp 7: sudo mount -a 8: mount
What you should see
user1@vm1:~$ cat /etc/fstab # /etc/fstab: static file system information. # # Use 'blkid' to print the universally unique identifier for a # device; this may be used with UUID= as a more robust way to name devices # that works even if disks are added and removed. See fstab(5). # # <file system> <mount point> <type> <options> <dump> <pass> proc /proc proc defaults 0 0 # / was on /dev/sda1 during installation UUID=05d469bb-dbfe-4d5a-9bb2-9c0fe9fa8577 / ext3 errors=remount-ro 0 1 # /home was on /dev/sda9 during installation UUID=a1b936a0-df38-4bf5-b095-6220ffdfc63c /home ext3 defaults 0 2 # /tmp was on /dev/sda8 during installation UUID=d0a86453-0dbb-4f33-a023-6c09fe9fa202 /tmp ext3 defaults 0 2 # /usr was on /dev/sda5 during installation UUID=b9544cbb-cdb6-4f3b-89e7-a339f52bfac7 /usr ext3 defaults 0 2 # /var was on /dev/sda6 during installation UUID=e15e713b-5850-4bc3-b99e-ab6f1d037caa /var ext3 defaults 0 2 # swap was on /dev/sda7 during installation UUID=4d516f09-80ff-4956-8a75-e9757697f6b1 none swap sw 0 0 /dev/scd0 /media/cdrom0 udf,iso9660 user,noauto 0 0 user1@vm1:~$ mount /dev/sda1 on / type ext3 (rw,errors=remount-ro) tmpfs on /lib/init/rw type tmpfs (rw,nosuid,mode=0755) proc on /proc type proc (rw,noexec,nosuid,nodev) sysfs on /sys type sysfs (rw,noexec,nosuid,nodev) udev on /dev type tmpfs (rw,mode=0755) tmpfs on /dev/shm type tmpfs (rw,nosuid,nodev) devpts on /dev/pts type devpts (rw,noexec,nosuid,gid=5,mode=620) /dev/sda9 on /home type ext3 (rw) /dev/sda5 on /usr type ext3 (rw) /dev/sda6 on /var type ext3 (rw) /dev/sda8 on /tmp type ext3 (rw) /dev/sda8 on /tmp type ext3 (rw) user1@vm1:~$ sudo blkid /dev/sda1: UUID="05d469bb-dbfe-4d5a-9bb2-9c0fe9fa8577" TYPE="ext3" /dev/sda5: UUID="b9544cbb-cdb6-4f3b-89e7-a339f52bfac7" TYPE="ext3" /dev/sda6: UUID="e15e713b-5850-4bc3-b99e-ab6f1d037caa" TYPE="ext3" /dev/sda7: UUID="4d516f09-80ff-4956-8a75-e9757697f6b1" TYPE="swap" /dev/sda8: UUID="d0a86453-0dbb-4f33-a023-6c09fe9fa202" TYPE="ext3" /dev/sda9: UUID="a1b936a0-df38-4bf5-b095-6220ffdfc63c" TYPE="ext3" user1@vm1:~$ sudo umount /tmp user1@vm1:~$ mount /dev/sda1 on / type ext3 (rw,errors=remount-ro) tmpfs on /lib/init/rw type tmpfs (rw,nosuid,mode=0755) proc on /proc type proc (rw,noexec,nosuid,nodev) sysfs on /sys type sysfs (rw,noexec,nosuid,nodev) udev on /dev type tmpfs (rw,mode=0755) tmpfs on /dev/shm type tmpfs (rw,nosuid,nodev) devpts on /dev/pts type devpts (rw,noexec,nosuid,gid=5,mode=620) /dev/sda9 on /home type ext3 (rw) /dev/sda5 on /usr type ext3 (rw) /dev/sda6 on /var type ext3 (rw) user1@vm1:~$ sudo fsck /tmp fsck from util-linux-ng 2.17.2 e2fsck 1.41.12 (17-May-2010) /dev/sda8: clean, 11/61752 files, 13973/246784 blocks user1@vm1:~$ sudo mount -a user1@vm1:~$ mount /dev/sda1 on / type ext3 (rw,errors=remount-ro) tmpfs on /lib/init/rw type tmpfs (rw,nosuid,mode=0755) proc on /proc type proc (rw,noexec,nosuid,nodev) sysfs on /sys type sysfs (rw,noexec,nosuid,nodev) udev on /dev type tmpfs (rw,mode=0755) tmpfs on /dev/shm type tmpfs (rw,nosuid,nodev) devpts on /dev/pts type devpts (rw,noexec,nosuid,gid=5,mode=620) /dev/sda9 on /home type ext3 (rw) /dev/sda5 on /usr type ext3 (rw) /dev/sda6 on /var type ext3 (rw) /dev/sda8 on /tmp type ext3 (rw) user1@vm1:~$
Explanation
- Prints out contents of your /etc/fstab file which contains information about your partitions and where to mount them.
- Prints out currently mounted partitions.
- Prints out UUIDs of all partitions in your system.
- Unmounts /tmp partition so you will be able to check it.
- Prints out currently mounted partitions once again. /tmp is now absent from this list.
- Check /tmp partition for errors. fsck knows which partition to check by reading corresponding /etc/fstab entry.
- Mounts all partitions described in /etc/fstab.
- Prints out currently mounted partitions yet another time. /tmp has returned to this list.
Extra credit
- Read man fstab, man mount.
