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

References

• [1] — A comprehensive analysis Backing up Linux and other Unix(-like) systems
  Recommends DAR. tar, rsync, rdiff-backup are also options
• [2] — [5] for using cpio in order to preserve hardlinks

BackupPC

Tools used by Phil Teuwen. Not used yet.

CloneZilla

Pro	Con
	Not a standalone program (only bootable cd / usb)

cpio

Some standard tool (see also [2] above).

DAR

Pro	Con
Single archive (containing all metadata)	transfer over network not easy. No immediate support for pipes (like ntfsclone)

DAR is recommended by [1] above. I personally tried the transfer through netword capability, but without success (broken image)

dump / restore

Backup tool for ext2/ext3 (/ext4 ?). See Backup or snaphot tool for ext4, but requires LVM2 for snapshot.

FSArchiver

Pro	Con
	* Does not support archiving through network (pipe). So one cannot save a partition, and restore it immediately on another machine through network for instance.

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
sudo mount -o remount,ro /dev/sda4                                         # To remount read-only if complain it is mounted already

ntfsclone

Pro	Con
Simple and fast output/input through pipes (for compression, network transfer) partition-2-partition cloning

Simply the best for ntfs backup (support partition-2-partition backup through network).

ntfsclone

Pro	Con
Single archive	No support for pipes (compression, transfer via network) Destination partition must be same size as source partition Lack support for some FS (partimage does not support ext4, partclone does not support reiserfs, despites what manual says)

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

rsync

Pro	Con
partition to partition cloning network support (using ssh). file-level backup, so can copy to a different filesystem type and size.	not a single archive. metadata stored as metadata in destination filesystem. complex set of options.

rsync goal is to synchronize 2 remote file systems over the network

My set of command line options (sudo pre-activation credits to [(credit http://crashingdaily.wordpress.com/2007/06/29/rsync-and-sudo-over-ssh/)] and [6])

#If needed, pre-activate sudo on remote system. Flag -t required to solve 'sudo: no tty present and no askpass program specified'
#
# Also, this requires the following line in /etc/sudoers:
#
#    Defaults     !tty_tickets
#
stty -echo; ssh -t user@server sudo -v; stty echo

sudo rsync -aHAXS --delete --rsync-path "sudo rsync" --numeric-ids -h -v --exclude='lost+found' user@server:/remote/path  /local/path
# -a, --archive           aka. preserve almost everything (equiv. to -rlptgoD, i.e. --recursive, --links, --perms, --times, 
#                         --group, --owner, --devices, --specials)
# -H, --hard-links        preserve hardlinks
# -A, --acls              preserve ACLs (implies --perms)
# -X, --xattrs            preserve extended attributes
# -S, --sparse            handle sparse file efficiently
# --delete                delete extraneous files from the receiving side
# --rsync-path            command executed on remote system
# --numeric-ids           use gid / uid instead of user/group name for file permissions
# -v, --verbose           display file while transfering
# --exclude='lost+found'  useful on ext3/ext4

Some options to consider adding:

# -z, --compress          might increase txf speed on slow network (internet)
# -h, --human-readable
# --stats
# -P                      equiv. to --partial --progress (quite verbose)
# -v -v                   more verbose

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. Also, moving or copying files ignore the sticky bit.

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'

However this does not work if files are copied or moved into the directory. In that case, files may either lose the group access flags, or even lose group ownership (see [7] for more). This could be a problem if for instance some application is unpacking some files in a temporary directory and then moves them to our ACL-controlled directory.

Change session primary group

We can change the primary group of the current session (and all sub-processes) so that any files created in the session belongs to some given group. This method is robust against moving / copying files into a directory, as long as these files have created in the same session. As a drawback however, it requires to first run a command to do the group switch:

See commands sg or newgrp.