Category: File system

How to Identify Your Linux File System Type.

To identify a Linux file system you can use the following standard command:
df -T or cat /etc/fstab or mount but the commands listed below are much more cool:

Use the file command.

root# file -sL /dev/sdc1
/dev/sdc1: sticky Linux rev 1.0 ext3 filesystem data, UUID=28d01367-3886-4f67-a3c9-447bf006ae27 (needs journal recovery) (errors) (large files)

root# file -sL /dev/sdc1
/dev/sdc1: sticky Linux rev 1.0 ext3 filesystem data, UUID=28d01367-3886-4f67-a3c9-447bf006ae27 (needs journal recovery) (errors) (large files)

Use the fsck command:

root# fsck -N /dev/sdc1
fsck from util-linux 2.20.1
[/sbin/fsck.ext3 (1) -- /mnt/data] fsck.ext3 /dev/sdc1

root# fsck -N /dev/zeus/root
fsck from util-linux 2.20.1
[/sbin/fsck.ext4 (1) -- /] fsck.ext4 /dev/mapper/zeus-root

How do I shrink the root logical volume (LV) on LVM?

The root partition and LV resizing should be done on unmounted partitions, so you have to boot from a rescue CD or USB stick, run it as live CD. Then make sure, that your root LV is not installed, by

mount

and unmount it when necessary. The LVM command vgchange changes attributes of volume groups. What needs to be “changed” to access the volume is the “availability” — i.e. to make the kernel realize the LVM volumes are there. This can be done by the command:

lvm vgchange -a y

Note, in rescue mode the system command is lvm and the LVM command that is run is vgchange. The -a y argument sets the availability to “y” or yes. As there are no specified LVM volume groups, this command will make all LVM volumes found available to the rescue kernel.

Once the kernel is aware of all LVM volumes they will be automatically mapped as devices. These are usually located under /dev/VolGroup or /dev/mapper/VolGroup (where “VolGroup” is the name of the Volume Group). Then do filesystem check

e2fsck -f /dev/yourVG/yourLV

on this LV. Then shrink filesystem

resize2fs /dev/yourVG/yourLV 5G

and reduce LV

lvreduce -L 5G /dev/yourVG/yourLV

Reboot to your system, Enjoy!

How to use bind mounts in Linux.

Bind mounting is quite simple. Instead of mounting a block device into a particular path you are mounting one path into another path.

mount -o bind /home/andzia /ftp/andzia

You will now see this reflected when running the mount command:

mount | grep var
/home/andzia on /ftp/andzia type none (rw,bind)

If you want this to persist across reboots, you’ll just need to update your /etc/fstab with the bind mount as well.

/home/andzia /ftp/andzia none bind 0 0

Using the dd command to determine sequential I/O speed.

The dd command provides a simple way to measure sequential I/O performance. The following shows a sequential read of 1GB (1024MB). There are 1024 1MB (1024KB) reads:

root:~# time -p dd if=/dev/zero of=2delete.file bs=1024k count=1024
1024+0 records in
1024+0 records out
1073741824 bytes (1.1 GB) copied, 17.5714 seconds, 61.1 MB/s
real 17.91
user 0.00
sys 2.62

The megabytes per second can be calculated as follows:

root:~: echo 1024 / 17.91 | bc
57

1GB/17.91 sec = 57 MBps

Access Control Lists aka ACLs for Linux file systems.

Traditionally, three permission sets are defined for each file object on a Linux system. These sets include the read (r), write (w), and execute (x) permissions for each of three types of users—the file owner, the group, and other users. In addition to that, it is possible to set the set user id, the set group id, and the sticky bit. This lean concept is fully adequate for most practical cases. However, for more complex scenarios or advanced applications, system administrators formerly had to use a number of workarounds to circumvent the limitations of the traditional permission concept.
Continue reading “Access Control Lists aka ACLs for Linux file systems.”

Display a directory as a web page.

Let’s say you want to allow someone access to files quickly via a web browser on your machine. You can do that with the help of python. All you do is change into the directory you want to serve up and then run the command:

python -m SimpleHTTPServer

Now, whoever needs to view that page simply points their browser to http://ADDRESS_OF_MACHINE:8000

Where ADDRESS_OF_MACHINE is either the IP Address or Domain of the machine (whichever applies). The user will then be able to navigate the files and folders within the directory you are serving up.

iSCSI – Initiator and Target.

The target is the name of the iSCSI server. The iSCSI server offers its devices (disks, tape, dvd/cd, etc.) to the clients. One device can by accessed by a few clients.

At first we have to set up a target server:

debian# apt-get install iscsitarget iscsitarget-dkms

then edit the configuration file:

debian# vi /etc/default/iscsitarget

and then, set ISCSITARGET_ENABLE to true: “ISCSITARGET_ENABLE=true“.

Now, we can create a volume group:

debian# vgcreate vg1 /dev/sdc1

but before that, you have to use fdiks to create Linux LVM partition. The next step is to initializes PhysicalVolume for later use by the Logical Volume Manager (LVM):

debian# pvcreate /dev/sdc1

and then, create a logical volume in an existing volume group:

debian# lvcreate -L2000M -n disk_sdc vg1

Now, we can add the “sdc1” disk to /etc/iet/ietd.conf and comment out everything in that file.


Target iqn.2012-10.com.home:disk.sdc
Lun 0 Path=/dev/vg1/disk_sdc,Type=fileio
Alias LUN1
MaxConnections 0

and then, and start the target:

debian# /etc/init.d/./iscsitarget start

The initiator is the name of the iSCSI client. The iSCSI client has a block level access to the iSCSI devices, which can be a disk, tape drive, DVD/CD writer. One client can use multiple iSCSI devices.

To install the initiator:

debian# apt-get install open-iscsi

and then, edit the /etc/iscsi/iscsid.conf file, and set node.srartup to automatic

node.startup = automatic

and then, restart the initiator:

debian# /etc/init.d/./open-iscsi restart

Discover targets using the discovery record with the recid matching the the discovery type and portal passed in. If there is no matching record, it will be created using the iscsid.conf discovery settings. This must be passed in discoverydb mode to instruct iscsiadm to perform discovery. This option is only valid for SendTargets discovery mode.

To do this:

debian# iscsiadm -m discovery -t st -p 192.168.1.100

output:

debian# iscsiadm -m discovery -t st -p 192.168.1.100
192.168.0.100:3260,1 iqn.2012-10.com.home:disk.sdc

Specify the mode. op must be one of discoverydb, node, fw, host iface or session.
If no other options are specified: for discoverydb and node, all of their respective records are displayed; for session, all active sessions and connections are displayed; for fw, all boot firmware values are displayed; for host, all iSCSI hosts are displayed; and for iface, all ifaces setup in /var/lib/iscsi/ifaces are displayed.

and then:

debian# iscsiadm -m node

and finally we can log in, either by running:

iscsiadm -m node --targetname "iqn.2012-10.com.home:disk.sdc" --portal "192.168.1.100:3260" --login

Ohh… that’s useful:

debian# cat /proc/net/iet/volume
debian# cat /proc/net/iet/vsession