Category: Linux

Load balancer

Load Balancer is used to distribute incoming traffic to multiple backend servers.

Here are some of the popular software load balancers

https://nginx.org/

http://www.haproxy.org/

https://containo.us/traefik/

August 21, 2020
CentovaCast change MySQL password
CentovaCast is a control panel to manage online streaming services. It support shoucast, liqudsoap and icecast streaming servers.

To change MySQL Password in CentovaCast, update following files.
```
/usr/local/centovacast/etc/centovacast.conf
```
You will see something like
```
# Enter your database connection information.
DB_NAME=centovacastdb
DB_USER=centovacast
DB_PASS=MySQLPasswordHere
DB_HOST=localhost
```
Following files is auto generated, this file also contain MySQL login details
```
/usr/local/centovacast/system/autoconfig.php
```
See CentovaCast
August 21, 2020

Can’t locate version.pm in @INC

I got error “Can’t locate version.pm in @INC” running awk.

[root@vmi431969 /]# ack mp3pdjSu5B0
Can't locate version.pm in @INC (@INC contains: /usr/local/lib64/perl5 /usr/local/share/perl5 /usr/lib64/perl5/vendor_perl /usr/share/perl5/vendor_perl /usr/lib64/perl5 /usr/share/perl5 .) at /usr/local/bin/ack line 18.
BEGIN failed--compilation aborted at /usr/local/bin/ack line 18.
[root@vmi431969 /]#

On CentOS, this error is fixed by running

yum install perl-version.x86_64 -y

See Errors

August 21, 2020

Wildcard DNS zone in bind
Wildcard DNS zone will act as authoritative DNS for any domain name. This is useful when you have a service like domain name parking service, where customers will change name servers of their domain name to your private label name servers. You need all thse domains get resolved to a specific IP address with out manually configuring DNS zone for each of the domain name.

Install Bind DNS server.

On Ubuntu/Debian
```
apt-get install bind9
```
On CentOS/RHEL
```
yum install bind9
```
Create a Catch-All zone file.
```
vi  /etc/bind/catch-all.zone
```
Add following content to the file
```
@ IN SOA ns1.yourdomain.com. hostmaster.yourdomain.com. ( 1 3h 1h 1w 1d )
  IN NS YOUR_IP_ADDR_HERE
* IN A YOUR_IP_ADDR_HERE
```
In above, replace

YOUR_IP_ADDR_HERE = IP you need all domains resolve to.
yourdomain.com = replace with your private label name server domain.

To make this zone active, you need to add it to named.conf, edit

On CentOS
```
vi  /etc/bind/named.conf.local
```
On Debian
```
vi  /etc/bind/named.conf
```
At the end of the file, add
```
zone "." IN {
        type master;
        file "/etc/bind/catch-all.zone";
};
```
Verify there is no error.
```
named-checkconf
```
Restart bind
```
systemctl restart bind9
```
Now verify Catch all DNS zone works with
```
nslookup serverok.in YOUR_DNS_SERVER_IP_HERE
```
It should resolve to the IP address specified in DNS zone file catch-all.zone. In above example, i used serverok.in for testing, you can use any domain, that should resolve to the IP address.

If you need to set MX rcord for the domains, you can add following to end of catch-all.zone file
```
  IN    MX      0       mx1.mail-server.com.
  IN    MX      5       mx2.mail-server.com.
```
See bind
August 19, 2020

Disable sshd start on boot in ubuntu

On my local computer, i have installed openssh-server, but i don’t want it always enabled.

To disable openssh-server from auto start on boot, run

systemctl disable ssh

Example

root@lab:~# systemctl disable ssh
Synchronizing state of ssh.service with SysV service script with /lib/systemd/systemd-sysv-install.
Executing: /lib/systemd/systemd-sysv-install disable ssh
Removed /etc/systemd/system/sshd.service.
Removed /etc/systemd/system/multi-user.target.wants/ssh.service.
root@lab:~#

If you want to start ssh server on boot, run systelctl enable ssh

root@lab:~# systemctl enable ssh
Synchronizing state of ssh.service with SysV service script with /lib/systemd/systemd-sysv-install.
Executing: /lib/systemd/systemd-sysv-install enable ssh
Created symlink /etc/systemd/system/sshd.service → /lib/systemd/system/ssh.service.
Created symlink /etc/systemd/system/multi-user.target.wants/ssh.service → /lib/systemd/system/ssh.service.
root@lab:~#

See Ubuntu

August 18, 2020

Upgrade centovacast

To upgrade centovacast installation, run

/usr/local/centovacast/sbin/update

centovacast

If you don’t want to upgrade shotcast/icecast/luquidsoap, you can run

for f in /usr/local/centovacast/etc/update.d/80*; do mv ${f} ${f}.disabled; done

This will disable updating these services. Sometimes newer version need a differnt config file, so maybe disabling updating these helps.

[root@centos7 ~]# cd  /usr/local/centovacast/etc/update.d/
[root@centos7 update.d]# ls -la
total 56
drwxr-x---. 2 root centovacast 4096 Dec  3 08:50 .
drwxr-x--x. 8 root centovacast 4096 Aug 17 01:03 ..
-rw-r-----. 1 root centovacast  117 Nov 18  2019 01_cc-common.update
-rw-r-----. 1 root centovacast  134 Nov 16  2019 30_cc-app.update
-rw-r-----. 1 root centovacast  105 Jun  2  2017 35_cc-imaged.update
-rw-r-----. 1 root centovacast  109 Sep 13  2019 35_cc-web.update
-rw-r-----. 1 root centovacast  114 Apr 28  2015 40_cc-comet.update
-rw-r-----. 1 root centovacast  129 Feb  7  2017 50_cc-control.update
-rw-r-----. 1 root centovacast  110 Jun  2  2017 75_cc-ftpd.update
-rw-r-----. 1 root centovacast  100 Oct  2  2015 80_cc-icecast.update.disabled.disabled
-rw-r-----. 1 root centovacast  109 Dec 26  2016 80_cc-liquidsoap.update.disabled.disabled
-rw-r-----. 1 root centovacast  108 Apr 14  2014 80_cc-sctrans2.update.disabled.disabled
-rw-r-----. 1 root centovacast  109 Apr 14  2014 80_cc-shoutcast1.update.disabled.disabled
-rw-r-----. 1 root centovacast  109 Apr 28  2015 80_cc-shoutcast2.update.disabled.disabled
[root@centos7 update.d]#

Updating centovacast

[root@centos7 ~]# /usr/local/centovacast/sbin/update

Checking Centova Cast Common Files ...
Downloading Centova Cast Common Files ...                                     

Verifying archive integrity ...                                               
Unpacking archive ...

Installing Centova Cast Common Files ...

Failed to execute operation: Connection timed out
Failed to start centovacast.service: Connection timed out
See system logs and 'systemctl status centovacast.service' for details.
Installation successful

Checking Centova Cast Application Server ...
Downloading Centova Cast Application Server ...                               

Verifying archive integrity ...                                               
Unpacking archive ...

Installing Centova Cast Application Server ...

Stopping any existing Centova Cast web service ...
Attempting to stop web: cc-web 
Stopping any existing Centova Cast application server service ...
Attempting to stop app: cc-appserver 
Upgrading database ...
OK
Installation successful
Starting Centova Cast application server service...
Attempting to start app: cc-appserver 
Re-starting Centova Cast web service ...
Attempting to start web: cc-web 

Checking Centova Cast Image Daemon ...
Not updated, skipping                                                         


Checking Centova Cast Web Server ...
Downloading Centova Cast Web Server ...                                       

Verifying archive integrity ...                                               
Unpacking archive ...

Installing Centova Cast Web Server ...

Stopping any existing Centova Cast web service ...
Attempting to stop web: cc-web 
Installation successful
Starting Centova Cast web service...
Attempting to start web: cc-web 

Checking Centova Cast Comet Daemon ...
Not updated, skipping                                                         


Checking Centova Cast Control Daemon ...
Not updated, skipping                                                         


Checking Centova Cast FTP Server ...
Not updated, skipping                                                         

[root@centos7 ~]#

See Centovacast

August 17, 2020

journalctl
To see systemd logs, run
```
journalctl -f
```
To see a service specific logs (example postfix)
```
journalctl -f -u postfix
```
To see logs for a specific service, run
```
journalctl --unit apache2
```
Logs with out pagination
```
journalctl --no-pager -u nginx
```
```
journalctl -u lxc-net.service -n 30
```
Change Disk used by journald

Modify file
```
vi /etc/systemd/journald.conf
```
Set disk usage limit by modifying value of SystemMaxUse
```
SystemMaxUse=500M
```
to free up disk,run
```
journalctl --vacuum-size=500M
```
See systemd
August 15, 2020

Install elasticsearch on CentOS 7

To install elasticsearch, first install java

yum -y install java-1.8.0-openjdk

Import key

rpm --import https://artifacts.elastic.co/GPG-KEY-elasticsearch

Create file

vi /etc/yum.repos.d/elasticsearch.repo

Paste following

[elasticsearch]
name=Elasticsearch repository for 7.x packages
baseurl=https://artifacts.elastic.co/packages/7.x/yum
gpgcheck=1
gpgkey=https://artifacts.elastic.co/GPG-KEY-elasticsearch
enabled=0
autorefresh=1
type=rpm-md

Install elasticsearch

yum install --enablerepo=elasticsearch elasticsearch

Set elastic search to start on boot

systemctl enable elasticsearch

To start/stop/status

systemctl stop elasticsearch.service
systemctl start elasticsearch.service
systemctl status elasticsearch.service

To see logs

tail -f /var/log/elasticsearch/elasticsearch.log

ElasticSearch runs on port 9200

[root@server ~]# netstat -lntp | grep java
tcp6       0      0 127.0.0.1:9200          :::*                    LISTEN      1289/java           
tcp6       0      0 ::1:9200                :::*                    LISTEN      1289/java           
tcp6       0      0 127.0.0.1:9300          :::*                    LISTEN      1289/java           
tcp6       0      0 ::1:9300                :::*                    LISTEN      1289/java           
[root@server ~]#

If you get error starting elasticsearch, check Elasticsearch failed to start on CentOS 7

If you have a previous installation, make sure you delete left over files before you install differnt version of elasticsearch. I removed following files/folders when i had to downgrade elasticsearch.

/etc/sysconfig/elasticsearch.rpmsave
/var/lib/elasticsearch
/var/log/elasticsearch

See elasticsearch

August 15, 2020

Change PHP version in Virtualmin Server
To change PHP version for a web site hosted in Virtualmin, click on the Virtualmin tab. Select the domain from drop down that you need to change PHP version for.
```
Virtualmin > YourDomain > Server Configuration > PHP Versions
```
On this page, select PHP version from drop down.

See Virtualmin
August 14, 2020
Protecting files with noclobber
To protect files on Linux by accidently overwritten by > operator, you can use
```
set -o noclobber
```
Now if you try to overwrite a file with >, you will get error
```
root@ok:~# echo "Hello" > 1.txt
-bash: 1.txt: cannot overwrite existing file
root@ok:~# 
```
If you really need to overwrite, use >! operator.
```
echo "Hello" >! FILE_NAME
```
Example
```
root@ok:~# echo "Hello" > 1.txt
-bash: 1.txt: cannot overwrite existing file
root@ok:~# echo "Hello" >! 1.txt
root@ok:~# 
```
Instead of running the command “set -o noclobber” everytime, you can add it to .bashrc file.
August 12, 2020
Extract Audio from Video using ffmpeg
To extract Audio from Video using ffmpeg, run
```
ffmpeg -i VIDEO_FILE.mp4 audio.mp3
```
August 12, 2020
Email Alert When User Login Using SSH
On web servers, you may need to get email alert when someone logs in to your server using SSH. To do this edit file
```
vi ~/.bashrc
```
Add
```
echo "ALERT - Bash shell access by user \"`whoami`\" to server $HOSTNAME  on  `date` "  | mail -s  "Alert:  Shell access detected from user \"`whoami`\" from IP_Address: `who | cut -d"(" -f2 | cut -d")" -f1`" you@your-domain.com
```
In above, replace you@your-domain.com with your actual email address. You need a mail server installed on your server for this to work.

If you want to log to a file, add
```
echo 'ALERT - Root Shell Access (' `hostname` ') on:' `date` `who` >> /var/log/user-logins
```
See SSH
August 11, 2020

Category: Linux

Change Disk used by journald