Adjusting filesystems with tune2fs
Editing Mount Options
Mount options are the parameters used when a filesystem is mounted at bootup or manually. They are turned on with the option
-o MOUNT-OPTION, MOUNT-OPTION
and turned off by adding a caret (^) before the mount option. Mount options on a filesystem are overwritten by mount options listed in /etc/fstab or by options to the mount command. Table 2 lists some of the most common mount options.
Table 2
Mount Options
| Option | Effect |
|---|---|
| debug |
Turns on debugging code. |
| bsdgroups |
New files take the group ID of their directory. |
| uid16 |
Disables 32-bit UIDs and GUIDs for older kernels that do not support them. |
| journal_data |
All data is added to the journal before being written into the main filesystem. |
| journal_data-writeback |
Only metadata is added to the journal before other data is written into the main filesystem. This option may allow old data to appear in files after a crash and journal recovery. |
| journal_data_ordered |
Data is written into the main filesystem before metadata is added to the journal. |
| nobarrier |
Writes to the journal; does not wait for all data to be committed first, which speeds performance but can prevent recovery from a journal.* |
| block_validity |
Extra checks are done after reading or writing from the filesystem.* |
| * Only ext4 filesystems. |
Working with Filesystems
Tune2fs is a powerful addition to the Linux administrator's toolkit. Here, I have tried to indicate its most useful features, but there is still no denying that the more you know about ext filesystems, the more you can appreciate its potential.
Assuming you are using systems installed in the last few years and are interested primarily in ext4 filesystems, I recommend that you start with the basic Wikipedia article [3] and then move on to the description of ext4 on the Linux Kernel Newbies site [4]. By the time you finish these articles, you should know enough to understand tune2fs more thoroughly.
A virtual machine is ideal for experimenting. You can also work on filesystems on your main system, but remember that the root filesystem – and, depending on your partitioning or logical volume model, possibly others – should only be edited when not mounted, which means booting from a Live device. If you are working on a mounted system, use the shell history so you can revert to the original settings easily. Work with an appreciation of the power of tune2fs, and you can learn its usefulness without creating any disasters for yourself.
Infos
- tune2fs: http://linux.die.net/man/8/tune2fs
- e2fsprogs: http://e2fsprogs.sourceforge.net/
- Wikipedia ext4 entry: https://en.wikipedia.org/wiki/Ext4
- Linux Kernel Newbies ext4 entry: http://kernelnewbies.org/Ext4
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