![Close [x]](http://dw1.s81c.com/i/c.gif){kind=small}
System recovery
The nicest thing about Linux from a maintenance perspective is that everything is a file. Of course, it can be perplexing at times to know which file something lives in. But as a rule, Linux recovery amounts to using basic filesystem utilities like cp, mv, and rm, and a text editor like vi. Of course, to automate these activities, tools like grep, awk, and bash are helpful; or at a higher level, perl or python. This tutorial does not address basic file manipulation.
Assuming you know how to manipulate and edit files, the only "gotcha" perhaps remaining for a broken system is not being able to use the filesystems at all.
Your best friend in repairing a broken filesystem is fsck. The next tutorial (on topic 203) has more information, so we will just introduce the tool here.
The tool called fsck is actually just a front-end for a number of more narrow fsck.* tools -- fsck.ext2, fsck.ext3, or fsck.reiser. You may specify the type explicitly using the -t option, but fsck will make an effort to figure it out on its own. Read the manpage for fsck or fsck.* for more details. The main thing you want to know is that the -a option will try to fix everything it can automatically.
You can check an unmounted filesystem by mentioning its raw device. For example, use fsck /dev/hda8 to check a partition not in use. You can also check a rooted filesystem such as fsck /home, but generally do that only if the filesystem is already mounted as read-only, not as read-write.
Mounting and unmounting with mount and umount
A flexible feature of Linux systems is the fine-tuned control you have over mounting and unmounting filesystems. Unlike under Windows and some other operating systems, partitions are not automatically assigned locations by the Linux kernel, but are instead attached to the single / root hierarchy by the mount command. Moreover, different filesystem types (on different drives, even) may be mounted within the same hierarchy. You can unmount a particular partition with the umount command, specifying either the mount point (such as /home) or the raw device (such as /dev/hda7).
For recovery purposes, the ability to control mount points lets you do forensic analysis on partitions -- using fsck or other tools -- without risk of further damage to a damaged filesystem. You may also custom mount a filesystem using various options; the most important of these is mounting read-only using either of the synonyms -r or -o ro.
As a quick example, you might want to substitute one user directory location for another, either because of damage to one or simply to expand disk space or move to a faster disk. You might perform this switch using something like:
# umount /home # old /dev/hda7 home dir
# mount -t xfs /dev/sda1 /home # new SCSI disk using XFS
# mount -t ext3 /dev/sda2 /tmp # also put the /tmp on SCSI
Mounting at bootup with /etc/fstab
For recovery, system upgrades, and special purposes, it is useful to be able to mount and unmount filesystems at will. But for day-to-day operation, you generally want a pretty fixed set of mounts to happen at every system boot. You control the mounts that happen at bootup by putting configuration lines in the file /etc/fstab. A typical configuration might look something like this:
Listing 4. Sample configuration in /etc/fstab
/dev/hda7 / ext3 defaults 1 1
none /dev/pts devpts mode=0620 0 0
/dev/hda9 /home ext3 defaults 1 2
none /mnt/cdrom supermount
dev=/dev/hdc,fs=auto,ro,--,iocharset=iso8859-1,codepage=850,umask=0 0 0
none /mnt/floppy supermount
dev=/dev/fd0,fs=auto,--,iocharset=iso8859-1,sync,codepage=850,umask=0 0 0
none /proc proc defaults 0 0
/dev/hda8 swap swap defaults 0 0
|
Find more details in the next tutorial (on topic 203).
Table of contents
Local resources
Tags
Use the slider bar to see more or fewer tags.
Popular tags shows the top tags for this particular content zone (for example, Java technology, Linux, WebSphere).
My tags shows your tags for this particular content zone (for example, Java technology, Linux, WebSphere).
Popular tutorial tags |
My tutorial tagsSkip to tags list
Popular tutorial tags |
My tutorial tags
