Category: Linux

  • Install dnsmasq on Ubuntu

    dnsmasq is a very powerful tool that can provide basic dns services/caching, act as dhcp server and also as tftp server.

    To install dnsmasq, run

    apt install dnsmasq

    When you start dnsmasq, if it complain about port 53 alreay in use

    dnsmasq: failed to create listening socket for port 53: Address already in use

    This is because some other service is running on port 53. To find what service is listening on port 53, run

    root@first-vm:~# netstat -lntp
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name    
tcp        0      0 0.0.0.0:2222            0.0.0.0:*               LISTEN      4934/sshd: /usr/sbi 
tcp        0      0 127.0.0.53:53           0.0.0.0:*               LISTEN      93/systemd-resolved 
tcp        0      0 127.0.0.1:3306          0.0.0.0:*               LISTEN      26081/mysqld        
tcp6       0      0 :::2222                 :::*                    LISTEN      4934/sshd: /usr/sbi 
tcp6       0      0 :::80                   :::*                    LISTEN      10467/apache2       
tcp6       0      0 :::3128                 :::*                    LISTEN      17606/(squid-1)     
root@first-vm:~#

    In this case, it is systemd-resolved. To stop it, run

    systemctl disable systemd-resolved
systemctl stop systemd-resolved

    Now you can start dnsmasq with

    systemctl start dnsmasq

    After starting dnsmasq, if you try resolve a domain, it will fail

    root@first-vm:~# nslookup yahoo.com localhost
;; connection timed out; no servers could be reached


root@first-vm:~#

    This is because default configuration don’t have anything enabled. To enable DNS caching/resolver, you need to edit file

    vi /etc/dnsmasq.conf

    Add line

    server=8.8.8.8
server=1.1.1.1

    Restart dnsmasq

    systemctl restart dnsmasq

    Now you will be able to resolve domain name using localhost as the dns server.

    root@first-vm:~# nslookup serverok.in localhost
Server:		localhost
Address:	::1#53

Non-authoritative answer:
Name:	serverok.in
Address: 172.67.133.148
Name:	serverok.in
Address: 104.21.14.2
Name:	serverok.in
Address: 2606:4700:3030::ac43:8594
Name:	serverok.in
Address: 2606:4700:3035::6815:e02

root@first-vm:~#

    If you need dnsmasq listen to only local ip, add following in /etc/dnsmasq.conf and restart dnsmasq.

    listen-address=127.0.0.1

    If you need to override MX record for a domain, you can add following to dnsmasq.conf

    mx-host=example.com,mail.example.com,5

    To set txt record for a domain

    txt-record=example.com,"v=spf1 a -all"

    See dnsmasq

  • oneinstack

    oneinstack is a free hosting management software available at

    https://oneinstack.com/

    Documentation available at

    https://oneinstack.com/docs/lampstack-image-guide-en/

    To find MySQL root password, run

    cd /root/oneinstack
grep dbrootpwd options.conf

    Nginx configuration files

    /usr/local/nginx/conf/vhost

    Restart Nginx

    systemctl restart nginx

    See Hosting Control Panels

  • geekbench

    To benchmark a server with GeekBench, you can run

    wget https://raw.githubusercontent.com/serverok/server-setup/master/benchmark/geekbench-6.sh
bash ./geekbench-6.sh

    You can create an account on https://browser.geekbench.com and keep all your benchmarks in one place. Here are my Geekbanch benchmarks

    https://browser.geekbench.com/user/55314

    If you get an error installing, you may need to install dependency with

    yum install libgcc.i386 libstdc++.i386 libgcc.i686 libstdc++.i686 -y

    How to Benchmark Cpanel server

    See Benchmark

  • aaPanel – Free Hosting Control Panel

    aaPanel is a free hosting control panel written in Python.

    https://www.aapanel.com/new/index.html
    install php redis extension in aaPanel

    Install aaPanel

    wget -O install.sh http://www.aapanel.com/script/install-ubuntu_6.0_en.sh && sudo bash install.sh forum

    Login url

    http://IP_ADDR:9514/login

    To reload nginx, run

    /www/server/nginx/sbin/nginx -s reload

    Nginx configuration file location

    /www/server/nginx/conf/nginx.conf
/www/server/panel/vhost/nginx/

    Web site files in

    /www/wwwroot/

    See Hosting Control Panel

  • runuser

    Linux Run Command as another user
    Install Xfce VNC remote desktop on Ubuntu

  • sudo

    Linux Run Command as another user
    usermod
    sudo: command not found

    To allow a user to run sudo commands without a password, run

    visudo

    Find

    %sudo   ALL=(ALL:ALL) ALL

    Add below

    USERNAME_HERE    ALL=(ALL:ALL) NOPASSWD:ALL

    This needs to be added after generic rules.

    Example

    boby    ALL=(ALL:ALL) NOPASSWD:ALL

  • Linux Run Command as another user

    To run command as another user on Linux, you can use

    su USER_NAME_HERE -s /bin/bash -c COMMAND_HERE

    Or

    sudo -u USER_NAME_HERE COMMAND_HERE

    Or

    runuser -l  USER_NAME_HERE -c 'COMMAND_HERE'

    See sudo

  • Bash check if a program is running or not

    You can find process id for a running program with command

    pidof BINARY_NAME_HERE

    Example

    boby@sok-01:~$ pidof gedit
22057
boby@sok-01:~$ ps aux | grep gedit
boby       22057  4.4  0.7 822760 60280 ?        Sl   14:29   0:00 /usr/bin/gedit --gapplication-service
boby       22071  0.0  0.0   8904   644 pts/0    S+   14:29   0:00 grep --color=auto gedit
boby@sok-01:~$

    We can use pidof command in bash script to find if a program is running or not

    if [ "$(pidof chrome)" ]
then
	echo "chrome already running."
fi

    See bash

  • Apache Solr

    How To Install Apache Solr on Debian 10

  • CWP not working after hostname SSL install

    On a CentOS Web Panel (CWP) server, control panel stopped working after installing SSL certficate for hostname.

    When starting cwpsrv service, i get following error.

    [root@nvme ~]# systemctl start cwpsrv
Job for cwpsrv.service failed because the control process exited with error code. See "systemctl status cwpsrv.service" and "journalctl -xe" for details.
[root@nvme ~]# systemctl status cwpsrv.service
● cwpsrv.service - CentOS Web Panel service (daemon)
   Loaded: loaded (/usr/lib/systemd/system/cwpsrv.service; enabled; vendor preset: disabled)
   Active: activating (auto-restart) (Result: exit-code) since Wed 2021-02-10 04:51:53 CET; 1s ago
  Process: 3779 ExecStartPre=/usr/local/cwpsrv/bin/cwpsrv -t (code=exited, status=1/FAILURE)

Feb 10 04:51:53 nvme.ssdnodo.com systemd[1]: Failed to start CentOS Web Panel service (daemon).
Feb 10 04:51:53 nvme.ssdnodo.com systemd[1]: Unit cwpsrv.service entered failed state.
Feb 10 04:51:53 nvme.ssdnodo.com systemd[1]: cwpsrv.service failed.
[root@nvme ~]# /usr/local/cwpsrv/bin/cwpsrv -t
cwpsrv: [emerg] annot load certificate key "/etc/pki/tls/private/hostname.key": BIO_new_file() failed (SSL: error:02001002:system library:fopen:No such file or directory:fopen('/etc/pki/tls/private/hostname.key','r') error:2006D080:BIO routines:BIO_new_file:no such file)
cwpsrv:configuration file /usr/local/cwpsrv/conf/cwpsrv.conf test failed
[root@nvme ~]#

    To fix this, i run

    /usr/local/cwpsrv/htdocs/resources/scripts/generate_hostname_ssl

    This generated the self signed SSL for hostname. After this CWP control panel started working.

    Apache still was down, fixed it by removing SSL virtualhost config for server hostname form folder

    /usr/local/apache/conf.d/vhosts/

    You can see hostname auto SSL logs at

    /var/log/cwp/autossl.log

    See CWP

  • Auto restart newrelic-daemon if crashed

    On a web server with Newrelic APM installed, graph stopped showing new data. On checking the newrelic log file, i get following error

    root@new-website-2:~# tail -f /var/log/newrelic/php_agent.log
2021-02-08 17:21:27.453 +0000 (680439 680439) warning: daemon connect(fd=13 uds=@newrelic) returned -1 errno=ECONNREFUSED. Failed to connect to the newrelic-daemon. Please make sure that there is a properly configured newrelic-daemon running. For additional assistance, please see: https://newrelic.com/docs/php/newrelic-daemon-startup-modes

    This is because newrelic-daemon stopped working. To auto restart newrelic-daemon if it crash, do the following

    mkdir -p /usr/serverok
vi /usr/serverok/newrelic

    Add following to the file

    #!/bin/bash
# Author: ServerOK
# Web: https://serverok.in/auto-restart-newrelic-daemon

CURRENT_STATUS="$(/etc/init.d/newrelic-daemon status)"

TIME_STAMP="$(date "+%Y-%m-%d %H:%M:%S")"

if [[ ! "${CURRENT_STATUS}" =~ "newrelic-daemon is running" ]]
then
    /etc/init.d/newrelic-daemon start
    echo -e "${TIME_STAMP} newrelic-daemon down\n"
fi

    Make the script executable

    chmod 755 /usr/serverok/newrelic

    Create a cronjob

    crontab -e

    Add following cronjob

    */5 * * * * /usr/serverok/newrelic > /var/log/newrelic/monitor.log 2>&1

    See Server Monitoring, Application Performance Monitor (APM)

  • bash check if a folder is empty or not

    To check if a folder is empty of not, you can use

    if [ "$(ls -A /home/boby/1/ )" ]
then
    echo "Files found"
else
    echo 'No files found'
fi

    If you want to reverse the checking, you can use !

    if [ ! "$(ls -A /home/boby/1/ )" ]
then
    echo "No files found"
else
    echo 'Files found.'
fi

    See bash