How can I upgrade to Debian GNU/Linux 6.0 (Squeeze) from the previous Debian 5.0 (Lenny) remotely?

The upgrades can be handled well by the command apt-get. Anyway before running the upgrade, it’s highly suggested to make a backup – at least the most important part of your system should be backup-ped. The official Debian document recommends:

The main things you’ll want to back up are the contents of /etc, /var/lib/dpkg, /var/lib/apt/extended_states and the output of dpkg –get-selections “*” (the quotes are important). If you use aptitude to manage packages on your system, you will also want to back up /var/lib/aptitude/pkgstates.

Let’s start the Debian Squeeze upgrade now. Firstly edit the file called /etc/apt/sources.list, enter:

# vi /etc/apt/sources.list

Replace the word “lenny” with “squeeze“, the it should look as follows:

deb http://ftp.us.debian.org/debian/ squeeze main
deb http://security.debian.org/ squeeze/updates main

These two lines are important for our upgrade, and you may have other lines inside, they don’t make much sense. Save and close the file. Type the following commands:

# apt-get update
# apt-get install apt dpkg aptitude
# apt-get dist-upgrade

When they all finish smoothly, it’s time to reboot the server. After a reboot make sure all services are running:

# lsb_release -a
# tail -f /var/log/messages

1, rcconf - http://packages.debian.org/lenny/rcconf

This tool configures system services in connection with system runlevels. It turns on/off services using the scripts in /etc/init.d/. Rcconf works with System-V style runlevel configuration. It is a Text User Interface (TUI) frontend to the update-rc.d command.

To start rcconf, login as root and type the command “rcconf“, then select the service that you would like to enable or disable, and press Tab to apply a change.

A similar command is sysv-rc-conf, you can make more specified choices in this TUI based configuration tool.

2, sysv-rc – http://packages.debian.org/lenny/sysv-rc

Sysv-rc provides a terminal interface for managing “/etc/rcX.d/” symlinks. With the help of update-rc.d, you can allow turning services on or off simply. Actually it’s much what chkconfig does in Redhat/CentOS, which means you can edit startup scripts for any runlevel.

By default sysv-rc is installed even in a minimal installation. Otherwise you need to run “apt-get install sysv-rc” to install it. Here’re some common usage examples for update-rc.d:

To remove the service SERVICE-NAME:

update-rc.d -f SERVICE-NAME remove

To add the service SERVICE-NAME:

update-rc.d SERVICE-NAME defaults

update-rc.d SERVICE-NAME defaults 29

The argument 29 is optional, which ensures that SERVICE-NAME is called after all scripts whose number is less than 29 have completed, and before all scripts whose number is 30 or greater.

To start the script SERVICE-NAME in runlevels 2345 and stop in 456, run (as root):

update-rc.d SERVICE-NAME start 2 3 4 5 . stop 0 1 6 .

update-rc.d SERVICE-NAME start 30 2 3 4 5 . stop 70 0 1 6 .

You can find more details of this command by running “man 8 update-rc.d”.

Someone probably will say that they can make a simple script in some minutes to do this kind of things. Actually you don’t need to recreate the wheel, the operating system have supplied such an utility already, the command is rename, it’s part of the util-linux package.

With the help of this command, it’s a very easy work to bulk rename files.
But, note that this command is a little different by systems.
Here we’ll show the usage examples for rename in both Redhat / CentOS and Debian / Ubuntu.

1, Batch rename files in Redhat / CentOS
For the scenario we mentioned above, it can be done like this:

$ rename .html .htm *

It renames all files in current working directory that match *.html* to *.htm*.
Note that only the first matched occurrence will be modified. If there’s a file called abc.html.abc.html, after renamed once, the new name is abc.htm.abc.html, not abc.html.abc.htm.

2, Bulk rename files in Debian / Ubuntu
The command here in Debian are quite different which makes it more powerful and professional.
I’ll show two examples with explaination:

$ rename -n 's/.html$/htm/' *

-n means no action will be applied, it will shows detailed information on what files would have been renamed:

$ rename -n 's/.html$/.htm/' abc.html.abc.html
abc.html.abc.html renamed as abc.html.abc.htm

The expression regunation here is in Perl style, which means you can apply multiple actions at one time, like this:

$ rename 's/.html$/htm/, s/css/css.backup/, s/jscript/js/' *

For more details you can raise a forum thread here at our support forum.

The general steps are:

• Stop the vserver in question

It can be done by this command: “vserver <server name> stop”

• Rename the /vservers/<server name> directory

By default it’s in /vservers, and on some self-crafted versions, it might be re-defined to other path like /var/lib/vservers. Simply you just need to use mv command to rename the issued vserver.

• Rename the /etc/vservers/<server name> directory

The directory /etc/vservers is much like a system wide configuration directory for vservers, you can use mv to rename specified directory as well.

• Update some softlink in /etc/vservers/<server name>

update link: /etc/vservers/<server name>/run -> /var/run/vservers/<server name>
update link: /etc/vservers/<server name>/vdir -> /etc/vservers/.defaults/vdirbase/<server name>
update link: /etc/vservers/<server name>/cache -> /etc/vservers/.defaults/cachebase/<server name>
Pay some attention to relative path issue, otherwise these links might get broken, there’s an example, the current working directory is /etc/vservers/mars:

joseph@galaxy:/etc/vservers/mars$ ln -s -f /etc/vservers/.defaults/vdirbase/mars vdir

• Update link: /var/run/vservers.rev/<server XID> -> /etc/vservers/<server name>

Please note that this just an update by fixing the dead link, and there’s no need to create a new XID.

• Reset hostname for vserver in question

Basically you just need to modify /etc/vservers/<server name>/uts/nodename before starting the issued vserver, and get other host name related settings modified when system booted.

joseph@galaxy:/etc/vservers$ grep mars -R mars/ 2>/dev/null -l
mars/uts/nodename
mars/vdir/etc/hosts
mars/vdir/etc/pam_ldap.conf
mars/vdir/etc/mailname
mars/vdir/etc/hostname

Now, It should start properly. If any issue encountered, please don’t hesitate to raise a forum thread at our community forum.

For example, when a Java environment is ready, we need to make sure that JAVA_HOME is globally available for some system accounts, so that they can restart java instance smoothly.

The following section would show an example on how to set the variable ORACLE_HOME to be a global one on both Debian and CentOS. Before we start, it’s suggested to have a glance on our former post “difference between login shell and non-login shell“.

Set system variables in Debian / Ubuntu

What is considered the best way to set globally exported environment variables in debian?  There are two ways:

For global settings, you can simply add a new line in /etc/environment like this:

ORACLE_HOME=/opt/oracle

After this modification, re-login is needed, then it would take effect for both login shell and non-login shells.

For a single user, you can apply this line in ~/.bashrc

export ORACLE_HOME=/opt/oracle

The above setting would take effect on both shells.
Normally, we just need to support login shells, so you can append the new line in /etc/profile. It would do the same work, BUT will not take effect on non-login shells.

Set global variables in CentOS / RHEL

There’s a standard way to set global environment variables on Redhat based systems, including Redhat 9.0, Fedora series, Red Hat Enterprise series, CentOS 4/5.
You can create a new file in /etc/profile.d/, and put the variables in it. This directory is used to store new variables:

example# ls /etc/profile.d/
colorls.csh  glib2.sh               krb5-devel.sh         lang.sh
colorls.sh   gnome-ssh-askpass.csh  krb5-workstation.csh  less.csh
cvs.sh       gnome-ssh-askpass.sh   krb5-workstation.sh   less.sh
glib2.csh    krb5-devel.csh         lang.csh              which-2.sh

The file you created should have a suffix “.sh”, so that it would be recognized as variable files by bash. No executable permission is needed for this new file. An example file is listed below:

example# cat oralce.sh
ORACLE_HOME=/opt/oracle

Note: All the above examples are assumed that you’re using BASH. If you use CSH as default shell, you should name this new file as “oracle.csh”, means the suffix should be “.csh”.

If you have any issue on this post, please leave a comment or raise a thread at our support forum, thanks!

Cpulimit is a simple program that attempts to limit the CPU usage of a process. It’s expressed in percentage, not in cpu time.

This is useful to control batch jobs, when you don’t want them to eat too much CPU resource. It does not act on the nice value or other scheduling priority stuff, but on the real CPU usage. Also, it is able to adapt itself to the overall system load, dynamically and quickly.

If your machine has one processor you can limit the percentage from 0% to 100%, which means that if you set for example 50%, your process cannot use more than 500 ms of cpu time for each second. But if your machine has four processors, percentage may vary from 0% to 400%, so setting the limit to 200% means to use no more than half of the available power. In any case, the percentage is the same of what you see when you run top.

Cpulimit should run at least with the same user running the controlled process. It’s much better if you run cpulimit as root, in order to have a higher priority and a more precise control.

Installation of CPUlimit

CPUlimit is available for Debian and Ubuntu, so it can be installed by “aptitude install cpulimit“. If you’re running CentOS or other system, you might need to compile it from source code by yourself.

After the installation, let’s take a look at the cpulimit man page to learn how to use it:

cpulimit TARGET [OPTIONS...]

TARGET must be exactly one of these:

-p, --pid=N              pid of the process
-e, --exe=FILE           name of the executable program file
-P, --path=PATH          absolute path name of the executable program file

OPTIONS
-l, --limit=N            percentage of CPU allowed from 0 to 100 (mandatory)
-v, --verbose            show control statistics
-z, --lazy               exit if there is no suitable target process, or if it dies
-h, --help               display this help and exit

Usage of CPUlimit

These examples are from CPUlimit man page as well:

Assuming  you  have  started "foo --bar" and you find out with top(1) or ps(1) that this process uses all your CPU time you can either

# cpulimit -e foo -l 50
limits the CPU usage of the process by acting on the executable program file. Note: the argument "--bar" is omitted.

# cpulimit -p 1234 -l 50
limits the CPU usage of the process by acting on its PID, as shown by ps(1)

# cpulimit -P /usr/bin/foo -l 50
same as -e but uses the absolute path name

Now let’s assume that we want to limit the process httpd to 45%. This is how we do it:

cpulimit -e httpd -l 45

The -e switch takes the name of the executable program file. You can take that name from the output of the top command.

Instead of using the name of the executable program file, we can use the process ID with the -p switch. You can find out the process ID of the httpd process as follows:

ps aux | grep httpd

Let’s assume the httpd process ID is 13500; we can then limit that process to 45% CPU usage as follows:

cpulimit -p 13500 -l 45

Instead of using the name of the executable file (-e) of the process ID (-p), we can also pass the absolute path name of the executable program file to cpulimit with the -P switch.

The absolute path name of the httpd executable is /usr/sbin/httpd so we’d use the following command:

cpulimit -P /usr/sbin/httpd -l 45

Please note that cpulimit will run in the foreground of your terminal until you terminate it with CTRL+C – terminating it will also remove any CPU limits.

Further Readings

CPUlimit Homepage:  http://cpulimit.sourceforge.net/

AND Homepage:  http://and.sourceforge.net/