FAQforge provides answers for frequently asked questions for the Linux-, MAC and Windows operating systems.
How to force caching headers with apache and squid reverse proxy
If you use a squid reverse proxy in front of your apache webserver to reduce the load, it might happen that pages are not cached correctly because the website script running on the apache webserver sends wrong caching headers. I had this problem with a wordpress install, wordpress had always send pragma no-cache headers with the pages so squid reported a cache miss for every page request. A simple solution for this is to use apache mod_headers to delete the no chache header and replace it with a header for 10 minute cache period.
First, ensure that mod_herders is enabled. To do this in Debian and Ubuntu, run the command:
a2enmod headers
Then create a .htaccess file in the website root directoyr which contains the following lines:
Header unset Pragma
Header set Cache-Control “must-revalidate, max-age=0, s-maxage=600″
Header set Vary “Accept-Encoding”
How to Update ISPConfig 3
The ISPConfig update script is a easy way to update a ISPConfig 3 installation. If you want to create a manual backup of ISPConfig, take a look at the instructions at the end of the article.
To update ISPConfig 3, login as root user on the shell of your server and run the command:
ispconfig_update.sh
>> Update
Please choose the update method. For production systems select ‘stable’.
The update from svn is only for development systems and may break your current setup.
Select update method (stable,svn) [stable]:
You should always select “stable” on a production system. The “svn” version is only suitable for ISPConfig 3 development.
The updater will then check the version of your system, download the latest update and starts the update process.
This application will update ISPConfig 3 on your server.
Shall the script create a ISPConfig backup in /var/backup/ now? (yes,no) [yes]:
You should choose “yes” here. This will create a backup of the ISPConfig scripts (/usr/local/ispconfig), the /etc directory and the ISPC0nfig MySQL database in the directory /var/backup/
Creating backup of “/usr/local/ispconfig” directory…
Creating backup of “/etc” directory…
Checking ISPConfig database .. OK
Starting incremental database update.
The update script will then start to install incremental database updates for ISPConfig, if required.
Reconfigure Permissions in master database? (yes,no) [no]:
If this is a slave server in a multiserver setup, then choose “yes” here on at least one of the slave servers. For single server installations, choose ‘no’. Then you were asked if the services shall be reconfigured:
Reconfigure Services? (yes,no) [yes]:
You should choose “yes” here, only if you modified your system configuration manually, it might be better to choose no. But in this case, new features in ISPConfig might not work or functions might stop working until you adjusted the config files manually. So its always a good choice to select ‘yes’ here. In the next step, select the ispconfig port:
ISPConfig Port [8080]:
Port 8080 is the default, if you have not changed it, press enter. Otherwise enter the port number and then press enter. As the last step, you wre asked if the crontab shall get reconfigured, you can select yes here by just pressing return.
Create new ISPConfig SSL certificate (yes,no) [no]:
If your SSL certificate for the ISPConfig interface has been expired and you want to renew it or if you want to enable SSL encryption for the ISPConfig interface, then choose “yes”. If you dont need a new SSL certificate, take the default (no).
Reconfigure Crontab? (yes,no) [yes]:
The ISPConfig updater will then update the ispconfig files and restart services, if the configuration has been changed.
Backup before updates
(This backup procedure is now integrated into the ISPConfig updater and gets executed automatically when you choose to create a backup during update)
Before you update a software, it is always a good idea to backup all relevant data. This enables you to restore the software version that you had before in case of an error. The steps to create a backup of the ispconfig software and settings are:
Create a backup folder:
mkdir /home/backup
chmod 700 /home/backup
cd /home/backup
Backup the database
mysqldump -u root -p dbispconfig > dbispconfig.sql
Backup the ISPConfig software
tar pcfz ispconfig_software.tar.gz /usr/local/ispconfig
Backup the configuration files in /etc
tar pcfz etc.tar.gz /etc
This backup does not include the emails and website data.
Rerun the last command with sudo on the Linux shell
Have you ever executed a command on the shell and noticed the that you had to run it with sudo? Instead of typing the command again with “sudo” in front of it, just run:
sudo !!
which will execute the command that was run before with sudo. Thanks to Planetfox for this tipp.
Keep the spamassassin filter rules up to date in ISPConfig 3
To update the spamassassin rules regularily on your ISPConfig 3 server, add the following line to the root crontab by running:
crontab -e
then insert the following line:
23 4 */2 * * /usr/bin/sa-update –no-gpg &> /dev/null
and save the file. The path to the sa-update script is /usr/bin/sa-update on Ubuntu and Debian Linux, if you use a different linux distrubution, run the command:
which sa-update
to find the location of the sa-update script and adjust the path in the crontab line above so that it matches the path on your system.
How to kill processes in “D” state in Linux?
If a process is shown with process state “D” in tools like ps or top, then its a zombie process. Example:
ps axl | grep D F UID PID PPID PRI NI VSZ RSS WCHAN STAT TTY TIME COMMAND 4 104 2579 9109 20 0 5024 2116 refrig D ? 0:00 cleanup -z -t unix -u -c
Zombie processes can not be killed with the normal commands like “kill -9 PID”, you will have to reboot the system to kill them.
How to use apt-file to find which .deb package contains a specific file
Sometimes you need to know which debian package contains a specific file e.g. because you deleted a system file accidently or you try to install a new software that requires this file. The apt package management utility which is used in Debian and Ubuntu comes with a handy tool called apt-file which allows a saerch for filenames in the package database.
Install apt-file
apt-get install apt-file
Update the apt-file database
apt-file update
Search for a specific file name, e.g. “lcrypto”
apt-file search /bin/bash
apt-file search /bin/bash
bash: /bin/bash
bash: /usr/bin/bashbug
bash-minimal: /bin/bash-minimal
bash-static: /bin/bash-static
bashdb: /usr/bin/bashdb
mybashburn: /usr/bin/bashburn
Calibrate the screen colors and gamma in Windows 7
To start the Windows 7 dccw application that calibrates the colors and gamma of your monitor, press the keys [Windows] + [R] to open the windows command line and enter:
dccw
Then click on “OK”.
and click on “next” and follow the instructions on the screen.
Robocopy single- and multithreaded benchmark on Windows 7
A commenter of my robocopy article asked me if a multithreaded copy tool like robocopy is really faster then a single threaded copy tool like xcopy as normally the harddisk is the bottleneck and not the CPU when copying files. As I did not found any benchmarks, I decided to do my own benchmark. Here are the results:
In my test, I copied a folder hierarchy with 429 directories and 6313 files with a overall size of 522 MB. I’ve run every test 2 times to ensure that the speed differences are not caused by filesystem caching. I know that this test was not made under scientific conditions, so if you have your own results, feel free to post them here as comment.
xcopy
Command:
xcopy D:\server\test D:\tmp\test /D /E /Y /Q
Time to copy files
First run: 42 seconds
Second run: 41 seconds
robocopy with 1 thread
Command:
robocopy D:\server\test D:\tmp\test /MT:1 /E /LOG:d:\tmp\robocopy.log
Time to copy the files
First run: 43 seconds
Second run: 41 seconds
robocopy with 10 threads
Command:
robocopy D:\server\test D:\tmp\test /MT:10 /E /LOG:d:\tmp\robocopy.log
Time to copy the files
First run: 38 seconds
Second run: 36 seconds
Conclusion: Using a multithreaded copy tool like robocopy with 10 threads speeds up file copying and makes sense if you have to copy a large number of files. At least on my system.
Copy files faster in Windows 7 with robocopy
Windows 7 comes with a new version of the robocopy command that is able to copy files much faster then the normal copy command or copy function of the file explorer by using several simultanious threads. So if you plan to copy a large number of files, e.g. to make a backup, use the robocopy command.
Example Copy files from C:\myFiles to F:\backup and use 10 simultanious threads. To execute robocopy, open the windows shell window or press the keys [Windows] + [R] to open the windows command line, then enter the command:
robocopy C:\myFiles F:\backup /MT:10
To get the full list of robocopy options, execute the command:
robocopy /?
For Windows XP or Vista, you can get the robocopy command from the Microsoft Resource Kit Tools
How to create a rescue CD in Windows 7
Windows 7 contains a application to create a rescue CD easily which can be used to boot the system and diagnose problems in Windows.
To create the rescue disc, press the keys [Windows] + [R] to open the windows command line and enter:
systemre