Archive for the ‘Linux & Unix’ Category
1.1 SCP Command Line-An Overview
The SCP command line is commonly used to copy files over SSH, and between popular Operating systems like Linux, Mac and Windows in a secure fashion. SCP is used to copy files to/from a remote server. It also allows you to copy files from one remote server to another remote server, without passing traffic through your PC.
When you get the error message "system-config-firewall: command not found" on your CentOS Server while trying to configure the firewall on the shell, then the text interface version of the firewall configuration utility is missing. Install it with this command:
yum install system-config-firewall-tui
If your mail server stops working (neither incoming nor outgoing email works) and you find the following error message in the mail.log file:
fatal: open database /var/lib/postfix/smtpd_scache.db: File exists
then the smtpd_scache.db might got corrupted. Postfix will recreate this file, if it does not exist. So it can be removed to solve the issue:
rm -f /var/lib/postfix/smtpd_scache.db
Thanks to Alexander Fox for sending me this FAQ.
Solution for dovecot error: /path/ is no longer mounted. If this is intentional, remove it with doveadm mount
Dovecot is watching the whole server filesystem for modifications and removed or added sub filesystems. If you get errors similar to this one on your server:
Aug 30 09:10:23 server1 dovecot: master: Warning: /var/www/clients/client1/web1/log is no longer mounted. If this is intentional, remove it with doveadm mount
(the directory path may vary), then you can fix it by excluding the path from being watched by dovecot. In my case, dovecot shall not watch my website directories as they do not contain any mailboxes
Run the following command on the shell as root user:
doveadm mount add '/var/www/*' ignore
To exclude all files and folders in /var/www from deovecot monitoring.
If you work on a dual boot system you might experience that when you log off from Windows, onto Linux, and to Windows again, the time that is shown in the bottom right corner might be an hour or more off the actual time. This will correct once you refresh it by loading the time from a time server again but will remain an issue for the next logins.
This has not directly to do with daylight savings or an incorrect time zone, but most likely with Linux assuming that the BIOS time is set to UTC while it's set to local time. So it just changes the BIOS clock according to that. Logging in to Windows with the wrong BIOS clock will result in a wrong system time.
This Linux behavior can easily be changed though, so just login to your Linux system and open a command line. First log in as root with your password:
Then enter following to open the rcS file (note that I use vi as text editor - you can use any other you like here):
Now look for the line reading UTC = yes and change it to UTC = no. Save the file and try to boot into Windows - if every other time setting is set correct you should get the right time now.
The past versions of Firefox brought a feature to it that a great deal of users didn't like because it changed the way tabs are handled in a window. Instead of just showing all tabs at once, Firefox now adds horizontal scrolling to the tab bar in order to prevent the tabs from becoming too small to read its name. That way you can always see what's on your tabs but don't have a complete overview of the whole bar anymore.
In order to help out on that an add-on was created that increases the number of tabs that are visible before the overflow scrolling occurs.
It's called Prevent Tab Overflow and you can find it in the Firefox Add-On database: https://addons.mozilla.org/en-US/firefox/addon/noverflow/
Add it and it will get to work instantly. Have a look at the Add-on preferences (Tools>Add-ons>Extensions>Prevent Tab Overflow>Preferences) to see what you can actually do:
While the add-on cannot prevent tab overflow as whole, it can resize the minimum tab width down to 40 pixel (the default in Firefox is 100 pixel). A lot more tabs fit in that way and the scrolling kicks in on a point where it actually makes sense not to shrink the tabs any further.
With Steam support for Linux, there will most likely be a whole lot more games coming out for Ubuntu and its consorts. While the database of games with Linux support still grows, many titles are already available.
To install Steam on Ubuntu or Linux Mint, open a Terminal and enter the following commands:
sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys B05498B7
sudo sh -c 'echo "deb http://repo.steampowered.com/steam/ precise steam" >>
sudo apt-get update
sudo apt-get install steam
Afterwards start it with
Solution for amavisd error – TROUBLE in process_request: Error writing a SMTP response to the socket: Broken pipe – on OpenVZ server
If you get error messages from amavisd similar to the one posted below on a server which is virtualized with OpenVZ:
Mar 5 09:09:02 v100 amavis: (17378-14) (!!)TROUBLE in process_request: Error writing a SMTP response to the socket: Broken pipe at (eval 100) line 987, <GEN44> line 31.
then the issue can be caused by the NUMTCPSOCK value in the openvz limits. Even if the barrier of this limit was never met in /proc/user_beancounters, the above error occurs when more then 25% of all TCP sockets were used. The solution is to set the NUMTCPSOCK barrier and limit to a high value in the openvz container configuration file. Here a value that worked for me on a moderately used mailserver:
Finally restart the OpenVZ VM to apply the new limit value.
If you use the apache mod_security module on your apache server, you might encounter wrong 403 errors for several URL's of the cms systems. Here are some exception rules to avoid that:
For WordPress Blogs
For the ModX CMS
SecRuleRemoveById 300013 300014 300015 300016
SecRuleRemoveById 300013 300016
Add these rules inside the vhost file of the website. If you use ISPConfig to manage the server, then add the rules in the apache directives field of the website settings in ispconfig.
Many thanks to PlanetFox for providing the rules.
Minecraft provides you with really good support on Linux. To be able to play, you need to download the .jar file from the official website first (you need that from the Minecraft for Linux / Other section: http://minecraft.net/download.
After you have it, you need to check if the java runtime environment is installed: open Synaptic Package Manager and search for the openjdk-7-jre package - if it isn't installed, install it now.
Head back to the downloaded minecraft.jar file. Right-click it and open the Properties. Go to the Permissions tab and check the Execute checkbox, close the window afterwards.
Now start minecraft by right-clicking the jar file again and selecting Open With >OpenJDK Java 7 Runtime - Enjoy Minecraft!