Linux Disk Management

Related pages

• Grub
• NTFS
• NFS
• ReiserFS
• Samba

Partitions

Some GUI software:

• gparted

Some CLI software:

• fdisk
• sfdisk
• parted

Some examples:

$ sudo fdisk -l /dev/sda                            # Show partition table for device /dev/sda
$ sudo fdisk -l -u /dev/sda                         # ... using sector as unit
$ sudo parted -l                                    # Show partition table of all devices
$ sudo parted /dev/sda print                        # ... of only device /dev/sda
$ sudo parted /dev/sda unit cyl print               #     ... using cylinder as unit
$ sudo parted /dev/sda unit s print                 #     ... using sector as unit (more accurate)
$ sudo sfdisk -l -uS /dev/sda                       # Show partition table for device /dev/sda
$ sudo sfdisk -d /dev/sda >sda-sfdisk.dump          # Dump partition in a format that can be understood by sfdisk
$ sudo sfdisk /dev/sda <sda-sfdisk.dump             # Restore a dumped partition table
$ sudo dd if=/dev/sda of=sda.mbr bs=512 count=1     # Save the complete MBR (table + boot code)

Use partprobe to force the kernel to re-read the MBR (re-read the partition table, see [1]). Or alternatively one can use fdisk to re-rewrite the same partition and force a re-read. And that are more solutions too ([2]):

$ sudo partprobe
# Or use fdisk
$ sudo fdisk /dev/sda
Command: v
Command: w
# Or use blockdev
$ sudo /sbin/blockdev --rereadpt /dev/hda
# Or use sfdisk
$ sudo sfdisk -R /dev/sda

Resizing Partitions

gparted

Probably one of the best way to edit/resize/move partition is to use the GUI tool gparted. It suports many different file systems, and allows for both resizing the file system but also updating the partition table.

If no GUI is available, here a few recipes for command-line.

Reiserfs

1. Use resize_reiserfs to resize the partition, and get the new partition size

resize_reiserfs -s -4G /dev/sda6               #Must be unmount
df

2. Change the partition table

sudo sfdisk -d /dev/sda >sda-sfdisk.dump          # Edit sda-sfdisk.dump

3. Run reiserfsck

sudo reiserfsck --rebuild-sb
sudo reiserfsck --fix-fixable

Mounting Partitions

See also reference pages above

Using /etc/fstab

Run sudo blkid to get the UUID number.

# NTFS
UUID=XXXXXXXXXXXXXXXXXXXXX /media/windows ntfs defaults,umask=007,gid=46 0 1

Partitions can then be mounted with mount <mount-point>

Using mount

# NTFS - mount point /media/windows must be chgrp plugdev
sudo mount -t ntfs -o defaults,umask=007,gid=46 /dev/sda1 /media/windows
# SAMBA
sudo mount -t cifs -o username=baddreams,uid=1000,gid=124 //phoenix/D$ /net/phoenix/d

Remounting root partition read-write

If /etc/fstab is corrupted, boot process might stop while root partition is mounted read-only. To remount it in read-write mode in order to fix /etc/fstab (see [3]):

mount -n -o remount,defaults /dev/sda1 /       # -n means do not update /etc/mtab (when /etc is ro)

Boost ext3/4 performance by enabling data writeback and disabling atime

Data writeback leads to faster performance on ext3/4 filesystem, at the cost of possible loss of new data in case of system crash (old data magically reappear) (see [4]). To enable it simply add data=writeback to mount options in /etc/fstab. Also disable update of atime (access time):

/dev/hda1 / ext3 defaults,errors=remount-ro,noatime,data=writeback 0 1

Unmount partition first! Either unmount the partition, or first run tune2fs to update the current mount flag:

tune2fs -o journal_data_writeback /dev/sda1

Backup

• FSArchiver

See this tutorial.

fsarchiver -v savefs /mnt/backupdrive/my-backup.fsa /dev/sda4
fsarchiver restfs -v /mnt/backupdrive/my-backup.fsa id=0,dest=/dev/sda4

• Bootable USB CloneZilla

• PartImage is another solution, but it does not support ext4.

• A comprehensive analysis Backing up Linux and other Unix(-like) systems — Dar or rsync are options.

• Dump, but requires LVM2 for snapshot.

• Using DAR.

• Using BackupPC.

RAMFS / TMPFS

References:

• http://www.thegeekstuff.com/2008/11/overview-of-ramfs-and-tmpfs-on-linux/
• http://en.wikipedia.org/wiki/Tmpfs

Using RAMFS and TMPFS you can allocate part of the physical memory to be used as a partition. This partition can be mounted as a regular hard disk partition to accelerate tasks that requires heavy disk access (this partition could store for instance a database, or a version control repository...)

Access Control

References:

• Part 1: How to work with Access Control Lists from the Command Line
• Part 2: How to work with Access Control Lists from the Command Line
• Using SGID to Control Group Ownership of Directories

Using SGID bit to Control Group Ownership

SGID bit allows for controlling the Group Ownership of files within a directory:

mkdir /data/testacl
chgrp git /data/testacl                # Set group to 'git'
chmod g+s /data/testacl                # Set SGID bit
cd /data/testacl
touch file                             # Now 'file' has group 'git', independently of current user primary group

This is nice, but access condition is still dependent on user's umask setting.

Using ACL to set default access control

ACL must be installed:

sudo apt-get install acl

... and enabled on the target file system in /etc/fstab:

/dev/sda7    /data     ext4      defaults,acl     0     2

Now, let's say that default permission is 'rwx' for file created in our 'test' directory above:

cd
setfacl -m d:group:git:rwx /data/testacl  # By default, all members of group 'git' will have rwx access
                                          # Independently of user's umask setting
umask 022
touch /data/testacl/file022               # File 'file022' is still writable for group 'git'