Category: Linux

How to disable GUI in Ubuntu
If you have installed Ubuntu with GUI and don’t want GUI, you can disable GUI from starting on boot with command
```
systemctl set-default multi-user
```
If you need to GUI auto-start on boot, run
```
systemctl set-default graphical.target
```
December 9, 2021
How to Setup Software RAID 0 on Linux Server
RAID 0 allows you to combine multiple disks into one large disk. Only use RAID 0 if the data is not important to you, for example, a backup server. If one disk fails in a RAID 0 array, all the data will be lost.

To create a software RAID 0 with 2 or more disks, first, we need to prepare the disks to be used as RAID members. Run the following commands on each of the disks we will be adding to the RAID 0 array.
```
parted /dev/sdX mklabel gpt
parted /dev/sdX mkpart primary ext4 0% 100%
parted /dev/sdX set 1 raid on
```
Replace /dev/sdX with actual device names and run the commands for all devices you will be adding to the RAID 0.

Create RAID 0

To create RAID 0, run the following command
```
mdadm --create --verbose /dev/md0 --raid-devices=2 --level=0 /dev/sdc1 /dev/sdd1
```
In the above command,

–raid-devices=2 = number of disks in the RAID. In this case, we have 2 disks. If you have more than 2 disks, change the number accordingly.

/dev/sdc1 /dev/sdd1 = device names, change it with your actual device names. If you have more devices, add them.

/dev/md0 = raid device name, it can be md0, md1, md2 etc..

Format RAID device

Before you can use RAID device, you need to format it.
```
mkfs.ext4 /dev/mdX
```
Replace /dev/mdX with your actual device name.

Updating mdadm.conf

Run
```
mdadm --detail --scan
```
It will print RAID definitions like the following example
```
root@grml ~ # mdadm --detail --scan
ARRAY /dev/md0 metadata=1.2 name=grml:0 UUID=44f0ec6b:f8311a0c:382295f8:d41fa0fe
root@grml ~ #  
```
You need to edit the file
```
vi /etc/mdadm/mdadm.conf 
```
Add the ARRAY definitions at end of the file. If any definitions are already there, don’t repeat them.

Mounting New RAID Device

Before you can mount RAID device, you need to find UUID for the raid device, this can be done with command
```
blkid
```
Example
```
root@grml ~ # blkid
/dev/loop0: TYPE="squashfs"
/dev/sda2: UUID="feacd62e-d23f-483d-8971-aa3f110fea05" TYPE="swap" PARTUUID="3019f70f-516a-493f-97cf-2aa001e1c574"
/dev/sda3: UUID="f162656d-bde9-4b14-8823-21e2a1618a2d" BLOCK_SIZE="4096" TYPE="ext4" PARTUUID="1fd4e63f-33a4-4c52-bc00-915c9d7965b8"
/dev/sda4: UUID="52ceb7c4-f065-4cc7-9c19-276a98be29a8" BLOCK_SIZE="4096" TYPE="ext4" PARTUUID="b8f92699-2892-482c-8abe-b90ca91b5fc0"
/dev/sdb1: UUID="44f0ec6b-f831-1a0c-3822-95f8d41fa0fe" UUID_SUB="65fd2c84-1217-2df7-2a2c-83046458805a" LABEL="grml:0" TYPE="linux_raid_member" PARTLABEL="primary" PARTUUID="b197077b-4a34-4459-8230-5c2a3b1c7085"
/dev/sdc1: UUID="44f0ec6b-f831-1a0c-3822-95f8d41fa0fe" UUID_SUB="fedb9e98-dd9f-daed-fc63-4f6a86ebfc9e" LABEL="grml:0" TYPE="linux_raid_member" PARTLABEL="primary" PARTUUID="807fda4f-d22b-4fa7-8810-839e68ae917e"
/dev/sdd1: UUID="44f0ec6b-f831-1a0c-3822-95f8d41fa0fe" UUID_SUB="071de57a-6d12-70e8-ed6d-cefe8371e915" LABEL="grml:0" TYPE="linux_raid_member" PARTLABEL="primary" PARTUUID="76f0cbbe-858a-4153-87dd-5665d1ac9939"
/dev/sda1: PARTUUID="9034a389-a6b2-424e-bd19-ce7e55561eba"
/dev/md0: UUID="9bd3d3ee-cc6b-43d5-91ed-627440cc9154" BLOCK_SIZE="4096" TYPE="ext4"
root@grml ~ # 
```
In this cause UUID for /dev/md0 is
```
UUID="9bd3d3ee-cc6b-43d5-91ed-627440cc9154"
```
Edit /etc/fstab
```
vi /etc/fstab
```
Add
```
UUID="9bd3d3ee-cc6b-43d5-91ed-627440cc9154"   /home  ext4    defaults  0       1
```
In the above

/home = is the mount point. If you need to mount the new RAID device as another folder, you need to create an empty directory first.

UUID=”9bd3d3ee-cc6b-43d5-91ed-627440cc9154″ = replace with your actual UUID.

Check status of raid

To see the status of the RAID, use the command
```
cat /proc/mdstat
```
Find RAID details

To find RAID details, use the following command
```
mdadm --detail /dev/mdX
```
Back to RAID
December 9, 2021

IO Load

To see which files cause IP load, use filetop

apt install -y bpfcc-tools
filetop-bpfcc -C

fatrace can list files that and currently used

apt install fatrace
fatrace --timestamp --filter=R
fatrace --timestamp --filter=W

totop

apt install iotop
iotop

To get IO read/write rate, run

sar -b 1 30

Example

root@server12:~# sar -b 1 30
Linux 2.6.32-754.18.2.el6.x86_64 (server12.hosthat.com) 	12/07/2021 	_x86_64_	(8 CPU)

08:47:15 PM       tps      rtps      wtps   bread/s   bwrtn/s
08:47:16 PM    121.00      0.00    121.00      0.00    940.00
08:47:17 PM      0.00      0.00      0.00      0.00      0.00
08:47:18 PM      6.06      6.06      0.00    549.49      0.00
08:47:19 PM      0.00      0.00      0.00      0.00      0.00
08:47:20 PM    204.95     11.88    193.07    174.26   2879.21
08:47:21 PM    579.38      2.06    577.32     16.49   4950.52
08:47:22 PM      2.04      0.00      2.04      0.00      2.04
08:47:23 PM      6.06      6.06      0.00     48.48      0.00
08:47:24 PM     50.51     50.51      0.00    694.95      0.00
08:47:25 PM    206.12     16.33    189.80    195.92   2746.94
08:47:26 PM   1239.39     30.30   1209.09    985.86  10927.27
08:47:27 PM    369.70      3.03    366.67     24.24   4906.06
08:47:28 PM      7.14      5.10      2.04     40.82      1.02
08:47:29 PM      0.00      0.00      0.00      0.00      0.00
08:47:30 PM    211.22      6.12    205.10     97.96   3114.29
08:47:31 PM    646.00      0.00    646.00      0.00   5426.00
08:47:32 PM     16.16     14.14      2.02    129.29      2.02
08:47:33 PM      0.00      0.00      0.00      0.00      0.00
08:47:34 PM      4.08      4.08      0.00     48.98      0.00
08:47:35 PM    216.00      2.00    214.00    512.00   3410.00
08:47:36 PM    448.00      8.00    440.00     96.00   3652.00
08:47:37 PM      2.06      0.00      2.06      0.00      2.06
08:47:38 PM      0.00      0.00      0.00      0.00      0.00
08:47:39 PM     10.10     10.10      0.00    177.78      0.00
08:47:40 PM    189.00      8.00    181.00    160.00   2650.00
08:47:41 PM    294.85      0.00    294.85      0.00   2420.62
08:47:42 PM      8.00      6.00      2.00     48.00      2.00
08:47:43 PM      2.02      2.02      0.00    517.17      0.00
08:47:44 PM     12.12     12.12      0.00    113.13      0.00
08:47:45 PM    179.59      6.12    173.47     65.31   2434.69
Average:       168.06      7.02    161.04    157.19   1686.36
root@server12:~#

To see system load, run

sar -u -o  1 30

December 7, 2021

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

Category: Linux

Create RAID 0

Format RAID device

Updating mdadm.conf

Mounting New RAID Device

Check status of raid

Find RAID details