Archive for the ‘CentOS’ Category
The easiets way to change the hostname on CentOS 7 is to use the hostnamectl command.
First I will check the current hostname by running "hostnamectl status" on the shell of my server:
The output on my system is:
[root@server1 ~]# hostnamectl status Static hostname: server1.example.com Icon name: computer-vm Chassis: vm Machine ID: d89865d34b5a4637a9a4ff0ce0f6da02 Boot ID: 56d1685056d743b39e57a7b9cbfe467c Virtualization: vmware Operating System: CentOS Linux 7 (Core) CPE OS Name: cpe:/o:centos:centos:7 Kernel: Linux 3.10.0-123.el7.x86_64 Architecture: x86_64
Then I change the hostname with the set-hostname option of the hostnamectl command to server2.example.com
hostnamectl set-hostname server2.example.com
Afterwats I check with the command hostname and hostname -f if the hostname change has succeeded.
The result should be:
[root@server1 ~]# hostname server2.example.com [root@server1 ~]# hostname -f server2.example.com
Instead of the hostname command you could also use the "hostnamectl status" command again to check if the new hostname has been set:
[root@server1 ~]# hostnamectl status Static hostname: server2.example.com Icon name: computer-vm Chassis: vm Machine ID: d89865d34b5a4637a9a4ff0ce0f6da02 Boot ID: 56d1685056d743b39e57a7b9cbfe467c Virtualization: vmware Operating System: CentOS Linux 7 (Core) CPE OS Name: cpe:/o:centos:centos:7 Kernel: Linux 3.10.0-123.el7.x86_64 Architecture: x86_64
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
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.
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.
The following guide shows how to disable and remove mysql replication from two or more mysql servers. These steps can be used for master/slave and master/master mysql setups. The following SQL commands have to be be executed in phpmyadmin or with the mysql commandline program. It is just important that you are logged in as mysql root user. Below I will use the mysql commandline client.
Login into mysql as root user from commandline:
mysql -u root -p
the mysql command will ask for the mysql root password.
Then execute these commands if the installed mysql version is < 5.5.16:
use the commands below instead if the mysql version is > 5.5.16
RESET SLAVE ALL;
Now edit the my.cnf file (/etc/mysql/my.cnf) and add a # in front of all lines that start with "replicate-" or "master-". Example:
# replicate-same-server-id = 0 # master-host = 192.168.0.105 # master-user = slaveuser # master-password = akst6Wqcz2B # master-connect-retry = 60
Then restart mysql:
The following guide describes the steps to add DNS records that route emails from a domain managed in ISPConfig 3 to google apps / gmail. The guide assumes that you have already setup the dns zone for your domain in ispconfig.
Login to ISPConfig, click on the DNS module icon in the upper navigation bar, then open the settings of the DNS zone that you want to redirect to google and click on the "records" tab. You should see a record list similar to this:
Now Delete the existing MX record and the "mail" A-Record. Then add the following new records:
example.com. ASPMX.L.GOOGLE.COM. 10
example.com. ALT1.ASPMX.L.GOOGLE.COM. 20
example.com. ALT2.ASPMX.L.GOOGLE.COM. 30
example.com. ASPMX2.GOOGLEMAIL.COM. 40
example.com. ASPMX3.GOOGLEMAIL.COM. 50
IMPORTANT: All full domain names like "ghs.google.com." have to end with a dot, if the dot is missing, the name is treated as subdomain of the zone.
The resulting record list should look like this:
Sometimes you are forced to compile packages from source because they are not present in your current distribution's package format, which can be really annoying. While this is the safer option, there is also a quicker alternative, which is converting existing packages into the one you need with alien.
sudo apt-get install alien
Before you use it, make sure to have read the alien man page!
If you're on Ubuntu for example and need a package that is only available in the rpm format, power your terminal and convert the package (the following is available as deb, it's just an example):
sudo alien clementine-1.0.1-1.fc16.x86_64.rpm
The package will then be converted. There are a few points that you should be aware of though:
- Dependencies of converted packages will not be resolved. If you install it anyway, your update manager may notice the missing dependencies and install them however.
- It is not recommended to use alien for critical packages. The man page gives further info on that.
The usual thing you find when you right-click your desktop to create a new document is the option to create an empty text document. This selection can be widened however by using the Templates folder in your home folder. Any document that is put in there will be selectable; this is also possible with pictures and other formats. Pinguy OS for example provides and excellent working system out of the box and comes with multiple file templates installed:
The string Untitled is put in front every newly created document from a template. To remove an item from the list, just remove it from your Templates folder. By making a document invisible in the Templates folder it is also removed from the list.