Table of Contents
When you are finished partitioning the hard disk, you can put a file system on each partition.
This chapter builds on the partitions from the previous chapter, and prepares you for the next one where we will mount the filesystems.
A file system is a way of organizing files on your partition. Besides file-based storage, file systems usually include directories and access control, and contain meta information about files like access times, modification times and file ownership.
The properties (length, character set, ...) of filenames are determined by the file system you choose. Directories are usually implemented as files, you will have to learn how this is implemented! Access control in file systems is tracked by user ownership (and group owner- and membership) in combination with one or more access control lists.
The Linux kernel will inform you about currently loaded file system drivers in /proc/filesystems.
root@rhel53 ~# cat /proc/filesystems | grep -v nodev ext2 iso9660 ext3
Once the most common Linux file systems is the ext2 (the second extended) file system. A disadvantage is that file system checks on ext2 can take a long time.
ext2 was being replaced by ext3 on most Linux machines. They are essentially the same, except for the journaling which is only present in ext3.
Journaling means that changes are first written to a journal on the disk. The journal is flushed regularly, writing the changes in the file system. Journaling keeps the file system in a consistent state, so you don't need a file system check after an unclean shutdown or power failure.
You can create these file systems with the /sbin/mkfs or /sbin/mke2fs commands. Use mke2fs -j to create an ext3 file system.
You can convert an ext2 to ext3 with tune2fs -j. You can mount an ext3 file system as ext2, but then you lose the journaling. Do not forget to run mkinitrd if you are booting from this device.
The newest incarnation of the ext file system is named ext4 and is available in the Linux kernel since 2008. ext4 supports larger files (up to 16 terabyte) and larger file systems than ext3 (and many more features).
Development started by making ext3 fully capable for 64-bit. When it turned out the changes were significant, the developers decided to name it ext4.
Redhat Enterprise Linux 7 will have XFS as the default file system. This is a highly scalable high-performance file system.
xfs was created for Irix and for a couple of years it was also used in FreeBSD. It is supported by the Linux kernel, but rarely used in dsitributions outside of the Redhat/CentOS realm.
The vfat file system exists in a couple of forms : fat12 for floppy disks, fat16 on ms-dos, and fat32 for larger disks. The Linux vfat implementation supports all of these, but vfat lacks a lot of features like security and links. fat disks can be read by every operating system, and are used a lot for digital cameras, usb sticks and to exchange data between different OS'ses on a home user's computer.
iso 9660 is the standard format for cdroms. Chances are you will encounter this file system also on your hard disk in the form of images of cdroms (often with the .iso extension). The iso 9660 standard limits filenames to the 8.3 format. The Unix world didn't like this, and thus added the rock ridge extensions, which allows for filenames up to 255 characters and Unix-style file-modes, ownership and symbolic links. Another extensions to iso 9660 is joliet, which adds 64 unicode characters to the filename. The el torito standard extends iso 9660 to be able to boot from CD-ROM's.
All things considered, swap is not a file system. But to use a partition as a swap partition it must be formatted and mounted as swap space.
You may encounter reiserfs on older Linux systems. Maybe you will see Sun's zfs or the open source btrfs. This last one requires a chapter on itself.
The /proc/filesystems file displays a list of supported file systems. When you mount a file system without explicitly defining one, then mount will first try to probe /etc/filesystems and then probe /proc/filesystems for all the filesystems without the nodev label. If /etc/filesystems ends with a line containing only an asterisk (*) then both files are probed.
paul@RHELv4u4:~$ cat /proc/filesystems
nodev sysfs
nodev rootfs
nodev bdev
nodev proc
nodev sockfs
nodev binfmt_misc
nodev usbfs
nodev usbdevfs
nodev futexfs
nodev tmpfs
nodev pipefs
nodev eventpollfs
nodev devpts
ext2
nodev ramfs
nodev hugetlbfs
iso9660
nodev relayfs
nodev mqueue
nodev selinuxfs
ext3
nodev rpc_pipefs
nodev vmware-hgfs
nodev autofs
paul@RHELv4u4:~$We now have a fresh partition. The system binaries to make file systems can be found with ls.
[root@RHEL4b ~]# ls -lS /sbin/mk* -rwxr-xr-x 3 root root 34832 Apr 24 2006 /sbin/mke2fs -rwxr-xr-x 3 root root 34832 Apr 24 2006 /sbin/mkfs.ext2 -rwxr-xr-x 3 root root 34832 Apr 24 2006 /sbin/mkfs.ext3 -rwxr-xr-x 3 root root 28484 Oct 13 2004 /sbin/mkdosfs -rwxr-xr-x 3 root root 28484 Oct 13 2004 /sbin/mkfs.msdos -rwxr-xr-x 3 root root 28484 Oct 13 2004 /sbin/mkfs.vfat -rwxr-xr-x 1 root root 20313 Apr 10 2006 /sbin/mkinitrd -rwxr-x--- 1 root root 15444 Oct 5 2004 /sbin/mkzonedb -rwxr-xr-x 1 root root 15300 May 24 2006 /sbin/mkfs.cramfs -rwxr-xr-x 1 root root 13036 May 24 2006 /sbin/mkswap -rwxr-xr-x 1 root root 6912 May 24 2006 /sbin/mkfs -rwxr-xr-x 1 root root 5905 Aug 3 2004 /sbin/mkbootdisk [root@RHEL4b ~]#
It is time for you to read the manual pages of mkfs and mke2fs. In the example below, you see the creation of an ext2 file system on /dev/sdb1. In real life, you might want to use options like -m0 and -j.
root@RHELv4u2:~# mke2fs /dev/sdb1 mke2fs 1.35 (28-Feb-2004) Filesystem label= OS type: Linux Block size=1024 (log=0) Fragment size=1024 (log=0) 28112 inodes, 112420 blocks 5621 blocks (5.00%) reserved for the super user First data block=1 Maximum filesystem blocks=67371008 14 block groups 8192 blocks per group, 8192 fragments per group 2008 inodes per group Superblock backups stored on blocks: 8193, 24577, 40961, 57345, 73729 Writing inode tables: done Writing superblocks and filesystem accounting information: done This filesystem will be automatically checked every 37 mounts or 180 days, whichever comes first. Use tune2fs -c or -i to override.
You can use tune2fs to list and set file system settings. The first screenshot lists the reserved space for root (which is set at five percent).
[root@rhel4 ~]# tune2fs -l /dev/sda1 | grep -i "block count" Block count: 104388 Reserved block count: 5219 [root@rhel4 ~]#
This example changes this value to ten percent. You can use tune2fs while the file system is active, even if it is the root file system (as in this example).
[root@rhel4 ~]# tune2fs -m10 /dev/sda1 tune2fs 1.35 (28-Feb-2004) Setting reserved blocks percentage to 10 (10430 blocks) [root@rhel4 ~]# tune2fs -l /dev/sda1 | grep -i "block count" Block count: 104388 Reserved block count: 10430 [root@rhel4 ~]#
The fsck command is a front end tool used to check a file system for errors.
[root@RHEL4b ~]# ls /sbin/*fsck* /sbin/dosfsck /sbin/fsck /sbin/fsck.ext2 /sbin/fsck.msdos /sbin/e2fsck /sbin/fsck.cramfs /sbin/fsck.ext3 /sbin/fsck.vfat [root@RHEL4b ~]#
The last column in /etc/fstab is used to determine whether a file system should be checked at boot-up.
[paul@RHEL4b ~]$ grep ext /etc/fstab /dev/VolGroup00/LogVol00 / ext3 defaults 1 1 LABEL=/boot /boot ext3 defaults 1 2 [paul@RHEL4b ~]$
Manually checking a mounted file system results in a warning from fsck.
[root@RHEL4b ~]# fsck /boot fsck 1.35 (28-Feb-2004) e2fsck 1.35 (28-Feb-2004) /dev/sda1 is mounted. WARNING!!! Running e2fsck on a mounted filesystem may cause SEVERE filesystem damage. Do you really want to continue (y/n)? no check aborted.
But after unmounting fsck and e2fsck can be used to check an ext2 file system.
[root@RHEL4b ~]# fsck /boot fsck 1.35 (28-Feb-2004) e2fsck 1.35 (28-Feb-2004) /boot: clean, 44/26104 files, 17598/104388 blocks [root@RHEL4b ~]# fsck -p /boot fsck 1.35 (28-Feb-2004) /boot: clean, 44/26104 files, 17598/104388 blocks [root@RHEL4b ~]# e2fsck -p /dev/sda1 /boot: clean, 44/26104 files, 17598/104388 blocks
1. List the filesystems that are known by your system.
2. Create an ext2 filesystem on the 200MB partition.
3. Create an ext3 filesystem on one of the 300MB logical drives.
4. Create an ext4 on the 400MB partition.
5. Set the reserved space for root on the ext3 filesystem to 0 percent.
6. Verify your work with fdisk and df.
7. Perform a file system check on all the new file systems.
1. List the filesystems that are known by your system.
man fs
cat /proc/filesystems
cat /etc/filesystems (not on all Linux distributions)
2. Create an ext2 filesystem on the 200MB partition.
mke2fs /dev/sdc1 (replace sdc1 with the correct partition)
3. Create an ext3 filesystem on one of the 300MB logical drives.
mke2fs -j /dev/sdb5 (replace sdb5 with the correct partition)
4. Create an ext4 on the 400MB partition.
mkfs.ext4 /dev/sdb1 (replace sdb1 with the correct partition)
5. Set the reserved space for root on the ext3 filesystem to 0 percent.
tune2fs -m 0 /dev/sdb5
6. Verify your work with fdisk and df.
mkfs (mke2fs) makes no difference in the output of these commands
The big change is in the next topic: mounting
7. Perform a file system check on all the new file systems.
fsck /dev/sdb1 fsck /dev/sdc1 fsck /dev/sdb5