Setting the Locale on Linux

A locale is a system setting that allows users to configure the operating system for their own language, date, currency, etc. on Linux. There are slightly different ways to set up locales on different Linux distributions. Here I write how I would normally set up locales on Linux.

To set the system-wide default locale, I would append the LANG= variable to the Linux kernel. The kernel will happily accept the LANG= variable and pass it to the operating system. With syslinux, I would have an entry in syslinux.cfg as follows.

LABEL debian
KERNEL vmlinuz-3.6.0
INITRD /boot/initramfs.lzma
APPEND LANG=en_US.UTF-8 TERM=vt100 root=/dev/sda9

On Debian, Ubuntu, Mint and MEPIS, the system-wide locale may be specified in /etc/environment or /etc/default/locale.

LANG=C.UTF-8

To set your own locale different from the system-wide locale, just add a line to your .bashrc or .xsession:

export LANG=zh_CN.UTF-8

Generating locale-archive Again

The number of locales available on the system may be incomplete in order to save disk space. To see which locales are available, run the following command:

locale -a

If you want to add or remove locales, edit /etc/locale.gen. The following is a sample locale.gen.

ar_SA.UTF-8 UTF-8
bn_IN UTF-8
de_DE.UTF-8 UTF-8
en_US ISO-8859-1
en_US.UTF-8 UTF-8
es_MX.UTF-8 UTF-8
fa_IR UTF-8
fr_FR.UTF-8 UTF-8
gu_IN UTF-8
hi_IN UTF-8
id_ID.UTF-8 UTF-8
it_IT.UTF-8 UTF-8
ja_JP.UTF-8 UTF-8
kn_IN UTF-8
ko_KR.UTF-8 UTF-8
ml_IN UTF-8
mr_IN UTF-8
or_IN UTF-8
pa_PK UTF-8
pt_BR.UTF-8 UTF-8
ru_RU.UTF-8 UTF-8
ta_IN UTF-8
te_IN UTF-8
th_TH.UTF-8 UTF-8
tr_TR.UTF-8 UTF-8
vi_VN UTF-8
zh_CN.UTF-8 UTF-8
zh_TW.UTF-8 UTF-8

After changing the file locale.gen, you need to run locale-gen to regenerate the file /usr/lib/locale/locale-archive.

locale-gen

Enabling All Possible Locales

If you have plenty disk space, then you can enable all locales supported by the current glibc implementation. The list of supported locales is at /usr/share/i18n/SUPPORTED. Just copy it to /etc/locale.gen and rebuild the locales. It will regenerate the file /usr/lib/locale/locale-archive to about 100MB.

cp /usr/share/i18n/SUPPORTED /etc/locale.gen
locale-gen

Running Applications In Different Locales

Use the env command to run an application in a different locale. For example, to run pidgin in Chinese on an English desktop, I would issue:

env LANG=zh_CN.UTF-8 pidgin

Disk Cloning / Imaging over Network with SSH, Netcat, DD and XZ

Today we have affordable, ample storage and faster bandwidth to facilitate partition imaging and disk cloning over network. Nowadays, it's common and feasible to take the image of a whole partition for various reasons. Compared to file-based backups using tar, disk imaging provides the following advantages.

• The boot sector is preserved so that it's easy to make it bootable after the restore.
  
• Information such as UUID and LABEL is presered, which helps identify the partition in booting and mounting.
  
• Information such as ACL and XATTR is preserved, which helps restrict file access and secure the system.
  
• Every bit in the unused sectors is preserved, which may assist in digital forensics to uncover deleted or hidden information.
  

There are commercial programs for disk imaging and backup (Norton Ghost, Acronis True Image). However, Linux users can use readily available tools to get things done. For disk cloning/imaging, we can use ssh, netcat, dd and xz. Note that dd will fail on physically damaged disks. For such disks, use ddrescue instead.

For security and compression, we are going to use ssh and xz in this tutorial. If you don't like xz, feel free to substitute xz with gzip, bzip2 or lzop. Also, netcat is used to stream the dd output over the network. On Debian and Ubuntu derivatives, you need the following packages.

• bzip2, gzip, lzop, lzma OR xz-utils
  
• dd
  
• netcat
  
• ssh
  

We are making these assumptions in the following scenarios.

• Sending computer S
  
  This computer has IP address 192.168.1.1 and needs to back up partition /dev/sda1.
  
• Sending Port
  
  We'll send using port 5525.
  
• Receiving computer T
  
  This computer has IP address 192.168.1.2 and needs to restore partition /dev/sda2.
  
• Receiving Port
  
  We'll receive at port 7749.
  

Disk Cloning using dd, xz, netcat and ssh

In this scenario, we will clone a disk partition, simultaneously sending an image of the source partition /dev/sda1 from computer S (192.168.1.1) and restoring it at /dev/sda2 on computer T (192.168.1.2). Make sure that the source partition is not mounted or is mounted read-only. Also, make sure that the target partition size is greater than or equal to the source partition size.

1. At the sending computer, compress the source partition /dev/sda1 with xz and set up netcat to send it at port 5525:
   
   

   dd if=/dev/sda1 bs=16M | xz | nc -l 5525

   
   
2. At the receiving computer, set up a SSH tunnel to the sending computer (192.168.1.1):
   
   

   ssh -f -N -L 7749:127.0.0.1:5525 username@192.168.1.1

   
   
3. At the receiving computer, type the following command to receive the partition image and restore it at /dev/sda2:
   
   

   nc 127.0.0.1 7749 | xz -d | dd of=/dev/sda2 bs=16M

   
   

Alternatively, we could take the following steps to achieve the same thing. However, we start at the receiving computer.

1. At the receiving computer with the target partition /dev/sda2, type the following command to receive the partition image:
   
   

   nc -l 7749 | xz -d | dd of=/dev/sda2 bs=16M

   
   
2. At the sending computer with the source partition /dev/sda1, set up a SSH tunnel to the receiving computer (192.168.1.2):
   
   

   ssh -f -N -L 5525:127.0.0.1:7749 username@192.168.1.2

   
   
3. At the sending computer, type the following command to compress the source partition /dev/sda1 and transmit it over the SSH tunnel:
   
   

   dd if=/dev/sda1 bs=16M | xz | nc 127.0.0.1 5525

   
   

   Note that the transfer may take many hours for a large partition.

   
   

Disk Imaging using dd, xz, netcat and ssh

In this scenario, we will just send an image of the source partition /dev/sda1 to the receiving computer T (192.168.1.2) without restoring it. Make sure that the source partition is not mounted or is mounted read-only. A question remains whether to compress the image at the sending or receiving computer. The answer depends on which computer is more powerful. For this example, we'll compress at the sending computer (for network bandwidth reason).

1. At the sending computer, compress the source partition /dev/sda1 with xz and stream it using netcat:
   
   

   dd if=/dev/sda1 bs=16M | xz | nc -l 5525

   
   
2. At the receiving computer, set up a SSH tunnel to the sending computer (192.168.1.1):
   
   

   ssh -f -N -L 7749:127.0.0.1:5525 username@192.168.1.1

   
   
3. At the receiving computer, type the following command to receive the file:
   
   

   nc 127.0.0.1 7749 > partimg.xz

   
   

Alternatively, we could take the following steps to achieve the same thing.

1. At the receiving computer, set up netcat to listen at port 7749 and save the incoming data to a file partimg.xz.
   
   

   nc -l 7749 | dd of=partimg.xz bs=16M

   
   
2. At the sending computer, establish a SSH tunnel to the receiving computer (192.168.1.2) first:
   
   

   ssh -f -N -L 5525:192.168.1.2:7749 username@192.168.1.2

   
   
3. At the sending computer, type the following command to compress the source partition /dev/sda1 and transmit it over the SSH tunnel:
   
   

   dd if=/dev/sda1 bs=16M | xz | nc 127.0.0.1 5525

   
   

   Note that the transfer may take many hours for a large partiiton.

   
   

Alternative Simple Commands for Disk Cloning / Imaging

I don't like these methods for some reason, but here I show the simpler methods where netcat is not needed. For disk cloning, type something like this:

dd if=/dev/sda1 bs=16M | xz | ssh username@192.168.1.2 "xz -d | dd of=/dev/sda2 bs=16M"

Just to send an image file, run a command as follows:

dd if=/dev/sda1 bs=16M | xz | ssh username@192.168.1.2 "dd of=partimg.xz bs=16M"

Also Read:

• Linux: Using dd To Back Up Hard Drive Partitions.
  
• Backing up Hard Disk Partitions in Linux
  

Checking Integrity of A Debian/Ubuntu System

Sometimes, a Linux filesystem becomes corrupted, system files are damaged, or some crucial files get lost. This often happens, regardless of which filesystem (ext2, ext3, ext4, jfs, reiserfs, reiser4, or xfs) is used. There are many possible reasons, such as:

• Unstable hardware, for example, memory or hard drive problem
  
• Overheat, power surge, quake or another environmental disaster
  
• Buggy software, such as a bug in the kernel or the filesystem driver
  
• Compromised security, for example, network intrusion or attack
  
• Worm or virus infection

Files in Linux systems can be categorized into the following three:

1. Verifiable System Files
   
   In Linux systems that are managed by packages (such as Debian and Ubuntu), these files are installed by packages and make up the bulk of the filesystem. These files reside in such directories as /bin, /lib, /sbin and /usr. They are usually static, which means they don't normally change except when the system is updated, or locally compiled binaries are installed.
   
2. Changeable System Files
   
   These files are auxiliary system files for system configuration, initialization or customization, and system data (such as logs and cache). They reside in /boot, /etc, /opt, /srv and /var.
   
3. User Data
   
   These files are created and used by superuser (a.k.a root) and normal users, or software-generated during casual user activities. Typically, they are in /home, /media, /mnt and /root.
   

This post focuses on verifiable system files (installed by packages). When the filesystem becomes corrupted (but not completely unreadable), it is possible to verify and restore the system integrity by using package checksums. Before you continue, make sure to fsck the filesystem.

e2fsck -r -v /dev/sda7

In this example, /dev/sda7 points to an ext2 partition we're going to check. Be aware that you cannot fsck a mounted filesystem. Therefore, boot with a Debian Live CD (or a Ubuntu CD) and run fsck. After you've performed fsck, there may be some files created in the /lost+found directory. We'll deal with them later. First, mount the filesystem.

mount -t ext2 /dev/sda7 /mnt

Go to /var/lib/dpkg/info. Then, concatenate all the md5sums files. Most, if not all, Debian and Ubuntu packages come with a md5sum file that we can use to check the integrity of the package and the files installed by the package.

cd /var/lib/dpkg/info
cat *.md5sums | sort > /dev/shm/all.md5

all.md5 has md5 checksums of all the files installed on the system. Now, check the files on the Debian/Ubuntu system against the concatenated md5sums file.

cd /
md5sum -c /dev/shm/all.md5 > /dev/shm/check.txt 2>&1

/dev/shm/check.txt now contains the results of the integrity check. It looks like this:

bin/bash: OK
bin/bunzip2: OK
bin/bzcat: FAILED

In this example, /bin/bzcat is damaged. To find all the missing or damaged files, use a command like this one:

grep -v ': OK$' /dev/shm/check.txt

Let's reinstall this file. First, find out which package this file belongs to.

dpkg -S /bin/bzcat

We'll see the following result.

bzip2: /bin/bzcat

Now we know that we need to reinstall bzip2. Let's download the package.

dpkg -p bzip2 | grep 'Filename: '

This command will let us know the name of the package to download. Use wget to download it.

wget ftp://ftp.us.debian.org/debian/pool/main/b/bzip2/bzip2_1.0.5-4_i386.deb

You can just reinstall the package.

dpkg -i bzip2_1.0.5-4_i386.deb

Or, you can just extract one file:

dpkg --fsys-tarfile bzip2_1.0.5-4_i386.deb | tar xf - ./bin/bzcat

Alternatively,

dpkg --fsys-tarfile bzip2_1.0.5-4_i386.deb | tar xOf - ./bin/bzcat > /mnt/bin/bzcat

To restore a file from the /lost+found directory, you can also use the MD5SUMS file. First, run md5sum on files in /lost+found.

cd /lost+found
md5sum *

You may get an output like this.

9aaa2176d20c1b1203e3abbac55a2513  #124531

To find out what #124531 file is originally, find its md5 checksum from the all.md5 file above.

grep 9aaa /dev/shm/all.md5

You'll get a result like this.

9aaa2176d20c1b1203e3abbac55a2513  bin/bzip2

Now you can just move it to its place.

mv \#124531 /mnt/bin/bzip2

After you restore all damaged files and restore files from /lost+found, you can find missing files in the system. Go to /var/lib/dpkg/info again and concatenate all the list files.

cd /var/lib/dpkg/info
cat *.list | sort | uniq > /dev/shm/all.txt

The .list files in the /var/lib/dpkg/info directore show the list of files installed by packages. Let's find what's missing from the system.

cd /
for f in $(cat /dev/shm/all.txt ); do test -e "$f" || echo "$f" >> /dev/shm/nonexist.txt ; done

The file /dev/shm/nonexist.txt will show which files are missing from the system. You can then replace the missing files as done previously.

MinGW, Cygwin: Building GNU Bash 4

Using MinGW and Cygwin in Windows ME, I kept getting the same errors:

[main] sh fork: child -1 died waiting for longjmp before initialization

sh fork: resource temporarily unavailable

I have no clue what causes this problem. I just hope that building GNU bash myself would solve this problem. So I downloaded the source for GNU Bash 4.0. Before beginning bash compilation, I made sure zlib, libiconv and gettext were all installed. To see how I compiled these 3 libraries, read the beginning of this post.

Then, I configured bash:

./configure --prefix=/ --enable-alias --enable-arith-for-command --enable-array-variables --enable-brace-expansion --enable-casemod-attributes --enable-casemod-expansions --enable-command-timing --enable-help-builtin --enable-history --enable-job-control --enable-multibyte --enable-prompt-string-decoding --enable-readline --disable-nls

make

make install

Text Conversion with sed

sed is a handy UNIX tool that manipulates a stream of text. Here I'll list some useful examples of sed commands. This is just a note to myself. I'll add more as I learn more about sed

To replace every instance of ABC with DEF in a text file, run the following command:

sed 's/ABC/DEF/g' input.txt > output.txt

To convert DOS/WINDOWS style text to UNIX/LINUX style text, run the following command. In other words, this command removes carriage returns from the end of every line:

sed 's/\r$//g' input.txt > output.txt

To remove a tab from the beginning of every line, run:

sed 's/^\t//g' input.txt > output.txt

Setting the Background with xsetbg

This is just my 2 cents on setting the wallpaper on your X Windows desktop. There are many tools for setting the background — technically called the root window. If you use KDE or GNOME, setting up the background is automatic as it is done by the friendly GUI. However, if you are one of those people — including me — who prefer light and minimalist X-Windows environment, you'll put a command in your .xsession file to set your background.

Here, I introduce you to a nice nifty tool called xsetbg. It belongs to a package called xloadimage. I find it attractive just because it doesn't have many dependencies. This is how I use xsetbg in my .xsession file to place my lotus wallpaper on the desktop:

/usr/bin/xsetbg -center -xzoom 115 -yzoom 128 /usr/share/pixmaps/5469_G.jpg

The nice thing about it is that it lets you zoom the width and height separately and center the image at the same time. Pratically, this feature allows you to hide unwanted edges from the screen. For example, the picture below has unnecessary edges around it.

The following command sets this image as the desktop wallpaper without the unwanted edges (assuming your screen is in 800x600 resolution). Change the zoom percentages as necessary for your screen resolution.

xsetbg -center -xzoom 67 -yzoom 85 Sanctuary.jpg