Category: Linux

View systemctl service file
To view the content of a systemd service file, run the command
```
systemctl cat SERVICE_NAME_HERE
```
Example

boby@sok-01:~$ systemctl cat nginx
# /lib/systemd/system/nginx.service
# Stop dance for nginx
# =======================
#
# ExecStop sends SIGSTOP (graceful stop) to the nginx process.
# If, after 5s (–retry QUIT/5) nginx is still running, systemd takes control
# and sends SIGTERM (fast shutdown) to the main process.
# After another 5s (TimeoutStopSec=5), and if nginx is alive, systemd sends
# SIGKILL to all the remaining processes in the process group (KillMode=mixed).
#
# nginx signals reference doc:
# http://nginx.org/en/docs/control.html
#
[Unit]
Description=A high performance web server and a reverse proxy server
Documentation=man:nginx(8)
After=network.target

[Service]
Type=forking
PIDFile=/run/nginx.pid
ExecStartPre=/usr/sbin/nginx -t -q -g ‘daemon on; master_process on;’
ExecStart=/usr/sbin/nginx -g ‘daemon on; master_process on;’
ExecReload=/usr/sbin/nginx -g ‘daemon on; master_process on;’ -s reload
ExecStop=-/sbin/start-stop-daemon –quiet –stop –retry QUIT/5 –pidfile /run/nginx.pid
TimeoutStopSec=5
KillMode=mixed

[Install]
WantedBy=multi-user.target
boby@sok-01:~$
December 2, 2021
Redis error currently not able to persist on disk
When doing a FLUSHALl on redis server, i get following error message

[root@server ~]# redis-cli FLUSHALL
(error) MISCONF Redis is configured to save RDB snapshots, but it is currently not able to persist on disk. Commands that may modify the data set are disabled, because this instance is configured to report errors during writes if RDB snapshotting fails (stop-writes-on-bgsave-error option). Please check the Redis logs for details about the RDB error.
[root@server ~]#

The error was because redis data directory was not properly configured.

To fix, the error, edit redis config file
```
vi /etc/redis/redis.conf
```
Find
```
dir ./
```
Replace with
```
dir /var/lib/redis
```
Create a directory
```
mkdir /var/lib/redis
```
Make it owned by user redis
```
chown redis:redis /var/lib/redis
```
Restart redis server
```
systemctl restart redis
```
See Redis
December 2, 2021
How to flush Redis cache
To delete everything from redis cache, run the command
```
redis-cli FLUSHDB
```
This will delete all keys from the current DB.

To delete cache from all DB, run
```
redis-cli FLUSHALL
```
If Redis is on another server or needs password, you can use the following command
```
redis-cli -h IP_HERE -p PORT_HERE -a PASSWORD_HERE FLUSHDB
```
See Redis
December 2, 2021

How to find Redis data directory

To find the data directory in redis, run the command

redis-cli config get dir

Redis data directory is specified in the configuration file

/etc/redis/redis.conf

The entry is

dir /var/lib/redis

redis data directory should be owned by user redis

chown redis:redis /var/lib/redis

Example

[root@server redis]# cd /var/lib/redis/
[root@server redis]# ls -la
total 12
drwxrwx---   2 redis redis 4096 Dec  2 06:44 .
drwxr-xr-x. 37 root  root  4096 Nov 20 17:30 ..
-rw-r--r--   1 redis redis   92 Dec  2 06:44 dump.rdb
[root@server redis]#

See Redis

December 2, 2021

How to Install Gnome and xRDP on RHEL 8 (CentOS 8/Alma Linux/Rocky Linux)
You can install Gnome Desktop + xdrp on a remote server (VPS/cloud or dedicated) and use it as a remote desktop for browsing or running applications. This instruction works for any RHEL 8 based distributions like CentOS 8, Alma Linux 8, Rocky Linux 8, and Oracle Linux 8.

Install Gnome Desktop with
```
dnf groupinstall -y --nobest Workstation
```
After installing, reboot the server
```
reboot
```
xrdp package is provided by epel repository, so let’s enable it with
```
dnf install -y epel-release
```
install xrdp
```
dnf install -y xrdp xrdp-selinux xorgxrdp
```
Enable and start xrdp
```
systemctl enable xrdp
systemctl start xrdp
```
Open port 3389 in the firewall
```
firewall-cmd --add-port=3389/tcp --permanent
firewall-cmd --reload
```
Create a user and set a password for the user. This user will be used to login to remote desktop
```
useradd -m --shell /bin/bash serverok
usermod -aG wheel serverok
passwd serverok
```
Now you should be able to login to remote desktop using RDP.

Once logged in, you may need to disable desktop animations to avoid lag by running the following command in the terminal.
```
gsettings set org.gnome.desktop.interface enable-animations false
```
December 1, 2021
Find files older than X minutes
To find files that are older than X minutes, use the command
```
find /path/ -type f -mmin +30
```
This will find all files inside /path/ that are older than 30 minutes.

If you need to delete those files, run
```
find /path/ -type f -mmin +30 -delete
```
To find files created in the last 30 minutes, run
```
find /path/ -type f -mmin 30
```
See find
November 30, 2021
Configure Failover IP in Ubuntu 20.04 OVH VPS
To configure IP on OVH VPS, you need to manually configure networking as OVH gateway is outside the failover IP subnet. For most hosting providers getaway will be in the same subnet as the IP address. To configure IP using netplan, see instruction here.

First, install ifupdown package
```
apt install -y ifupdown
```
Now edit file
```
vi /etc/network/interfaces
```
Add
```
auto NETWORK_INTERFACE_HERE
iface NETWORK_INTERFACE_HERE inet static
    address FO_IP_ADDR
    netmask 255.255.255.255
    broadcast FO_IP_ADDR
    dns-nameservers 8.8.8.8 8.8.4.4
    post-up ip route add GATEWAY_ADDR dev NETWORK_INTERFACE_HERE
    post-up ip route add default via GATEWAY_ADDR dev NETWORK_INTERFACE_HERE
    pre-down ip route del GATEWAY_ADDR dev NETWORK_INTERFACE_HERE
    pre-down ip route del default via GATEWAY_ADDR dev NETWORK_INTERFACE_HERE
```
In the above text, replace

NETWORK_INTERFACE_HERE = with your actual network interface name, for example, eth0, ens18, etc.
FO_IP_ADDR = Your VPS IP address, OVH calls this Failover IP address. It is just any secondary IP address you purchase.
GATEWAY_ADDR = Gateway IP address. This is the same as the Main IP of the server with the last octal replaced by 254

Example

Configuration is the same as Ubuntu 18.04, the only difference is post-up and pre-down tines, where Ubuntu 18.04 used older route command, in Ubuntu 20.04, we use “ip route” command instead.
November 26, 2021
Bitnami WordPress Failed to update Plugin
On a Bitnami WordPress server, plugin installation/upgrade failed with permission error. The error is because the web server in bitmai servers runs as user daemon. When you upload a file as user bitnami, you need to make sure you set file permission properly so anyone in the group can write.

To fix the error, run
```
sudo chown -R bitnami:daemon /home/bitnami/stack/wordpress
sudo chown -R bitnami:daemon /bitnami/wordpress/wp-content
sudo chmod -R 770 /bitnami/wordpress/wp-content
sudo chmod -R 770 /home/bitnami/stack/wordpress
```
Some bitnami installations use different file structure
```
sudo chown -R bitnami:daemon /home/bitnami/apps/wordpress/htdocs
sudo chmod -R 770 /home/bitnami/apps/wordpress/htdocs
```
in wp-config.php, added the following when I migrated a site, refer to original wp-config.php for your exact path
```
define('FS_METHOD', 'direct');
define('WP_TEMP_DIR', '/opt/bitnami/apps/wordpress/tmp');
```
November 25, 2021

Install latest Redis on Ubuntu/Debian Server

To install the latest version of Redis on Ubuntu/Debian server, run

curl https://packages.redis.io/gpg | sudo apt-key add -
echo "deb https://packages.redis.io/deb $(lsb_release -cs) main" | sudo tee /etc/apt/sources.list.d/redis.list
sudo apt-get update
sudo apt-get install redis

Enable redis server to start on boot

systemctl enable redis-server

Start redis server

systemctl start redis-server

See Redis

November 22, 2021

nuster

Configure multiple SSL certificates in nuster

Back to Reverse Proxy

November 22, 2021
How to Install PHP 5.6 on Oracle Linux 7
Oracle Linux is a free RHEL based Linux distro. We will install PHP 5.6 on an Oracle Linux 7 server.

First, enable EPEL repo
```
yum install https://dl.fedoraproject.org/pub/epel/epel-release-latest-7.noarch.rpm
```
Enable Remi repo
```
yum install http://rpms.remirepo.net/enterprise/remi-release-7.rpm
```
Install yum-utils package
```
yum install yum-utils
```
Enable remi-php56
```
yum-config-manager --enable remi-php56
```
Install PHP 5.6 with
```
yum install -y php php-bcmath php-cli php-common php-devel php-gd \
    php-imap php-intl php-json php-ldap php-lz4 php-mbstring php-mysqlnd \
    php-soap php-intl php-opcache php-xml php-pdo
```
This will only install the CLI version of PHP 5.6. To make Apache work with PHP 5.6, install
```
yum install php-pecl-http.x86_64
```
This will create file /etc/httpd/conf.d/php.conf, that enable PHP module in Apache.

Restart apache webserver
```
systemctl restart httpd
```
Now Apache will be able to serve PHP files.
November 6, 2021

Install Jenkins on Ubuntu

Jenkins is an open source automation server. It helps automate the parts of software development related to building, testing, and deploying, facilitating continuous integration and continuous delivery.

Jenkins is a Java Application. So you need to install JRE (Java Runtime Environment). Install it with

sudo apt-get install default-jre

You can find instructions for installing Jenkins on Debian/Ubuntu at

https://pkg.jenkins.io/debian-stable/

Install Jenkins

wget -q -O - https://pkg.jenkins.io/debian-stable/jenkins.io.key | sudo apt-key add -
sudo sh -c 'echo deb https://pkg.jenkins.io/debian-stable binary/ > /etc/apt/sources.list.d/jenkins.list'
sudo apt-get update
sudo apt-get install jenkins

Enable Jenkins to start on boot

sudo systemctl enable jenkins

Start Jenkins

sudo systemctl start jenkins

To check status

sudo systemctl status jenkins

You can verify Jenkins running on port 8080 with command

root@jenkins:~# netstat -lntp
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address           Foreign Address         State       PID/Program name    
tcp        0      0 127.0.0.53:53           0.0.0.0:*               LISTEN      186/systemd-resolve 
tcp        0      0 0.0.0.0:22              0.0.0.0:*               LISTEN      256/sshd: /usr/sbin 
tcp6       0      0 :::22                   :::*                    LISTEN      256/sshd: /usr/sbin 
tcp6       0      0 :::8080                 :::*                    LISTEN      4774/java           
root@jenkins:~#

To find the initial password, run the command

cat /var/lib/jenkins/secrets/initialAdminPassword

November 5, 2021