Category: Linux

Installing r1soft server backup agent on Debian/Ubuntu

To install r1soft server backup agent on Ubuntu/Debian, add repository

echo deb http://repo.r1soft.com/apt stable main >> /etc/apt/sources.list
wget http://repo.r1soft.com/r1soft.asc
apt-key add r1soft.asc

Install agent

apt update
apt -y install serverbackup-enterprise-agent

Install kernal headers

apt install linux-headers-`uname -r`

Install kernal modules

serverbackup-setup --get-module

Verify backup agent works with

serverbackup-setup --test-connection

Start backup agent

/etc/init.d/cdp-agent restart

Now you can add the server to R1Soft Backup Manager.

June 19, 2019

Set default PHP version in Ubuntu

To select default PHP version in Ubuntu, run

update-alternatives --config  php

This will show a menu, you can select the default php version

root@server:/usr/bin# update-alternatives --config  php
There are 2 choices for the alternative php (providing /usr/bin/php).

  Selection    Path             Priority   Status
------------------------------------------------------------
* 0            /usr/bin/php7.0   70        auto mode
  1            /usr/bin/php5.6   56        manual mode
  2            /usr/bin/php7.0   70        manual mode

Press  to keep the current choice[*], or type selection number: 1
update-alternatives: using /usr/bin/php5.6 to provide /usr/bin/php (php) in manual mode
root@server:/usr/bin#

After setting PHP 5.6 as default PHP version, you will see

root@server:~# php -v
PHP 5.6.40-8+0~20190531120521.15+stretch~1.gbpa77d1d (cli) 
Copyright (c) 1997-2016 The PHP Group
Zend Engine v2.6.0, Copyright (c) 1998-2016 Zend Technologies
    with Zend OPcache v7.0.6-dev, Copyright (c) 1999-2016, by Zend Technologies
root@server:~#

June 18, 2019

Install Transmission torrent client on Ubuntu Server
To install transmission torrent client on Ubuntu, run
```
apt install transmission-cli transmission-common transmission-daemon
```
Before you can configure transmission-deamon, you need to stop it.
```
service transmission-daemon stop
```
Edit configuration file
```
vi /var/lib/transmission-daemon/info/settings.json
```
Once edited, start transmission-deamon with
```
service transmission-daemon start
```
Settings Password

Default user and password is “transmission”.

You can modify it by editing config file
```
"rpc-password": "{62b16db87b89a91dd49a5110a7cafc06d20eb4f2wtK6kqPj",
"rpc-username": "transmission",
```
Password you can use plain text. Transmission will convert it to SHA1 encrypted format on startup,

Allow remote access

You need to put your IP
```
"rpc-whitelist": "127.0.0.1,192.168.*.*",
```
Only white listed IP can access the web interface.

Download folder

By default download will be stored in folder
```
"download-dir": "/var/lib/transmission-daemon/downloads",
```
You can modify this folder as required.

Web interface

Web interface can be accessed using port 9091.
```
http://SERVER-IP:9091
```
June 18, 2019
linux

CentOS
Ubuntu
Debian
ArchLinux
openSUSE

Try Linux distro with out downloading ISO

June 17, 2019
Try Linux distro with out downloading ISO

You can try various linux distributions with out downloading ISO. To try, go to web site

https://distrotest.net

Find the linux distribition from the list of available operating systems.

On next page, you will get IP address and port, that you can use to connect to the system using VNC viewer. There is option for using web based VNC client, this will open the desktop on a new browser window.

June 17, 2019
run same command on multiple tmux panes
If you want to run same command on multiple servers, you can use tmux synchronize-panes feature. This will be useful when you need to setup multiple servers, say install nginx/php/mysql on multiple servers.

You can create multiple panes in tmux. SSH into each of the servers from these panes. Now run
```
CTRL + B :
```
Now type
```
setw synchronize-panes on
```
Whatever command you run on one of the pane will be executed on all panes. Be careful when you run server specific commands.
June 11, 2019
tmux create new window on current directory
When you start a new window or split pane on tmux, it always start with the directory from where you run tmux command.

I prefer it start with current working directory of active tmux window. To do this, edit file
```
vi ~/.tmux.conf
```
Add
```
bind c new-window -c "#{pane_current_path}"
bind '"' split-window -c "#{pane_current_path}"
bind % split-window -h -c "#{pane_current_path}"
```
June 8, 2019

Auto Attach to tmux session on SSH

To start tmux and attach to existing connection on SSH in, edit file

vi ~/.bashrc

Add

if [[ "$TMUX" == "" ]] && [[ "$SSH_CONNECTION" != "" ]] && [ "$SSH_TTY" != "" ]; then
    WHOAMI=$(whoami)
    if tmux has-session -t $WHOAMI 2>/dev/null; then
        tmux -2 attach-session -t $WHOAMI
    else
        tmux -2 new-session -s $WHOAMI
    fi
fi

Method 2

You can use following command when connecting to remote sevrer.

ssh  USER@SERVER_IP -t tmux a

June 8, 2019

Install MongoDB 4.0 on CentOS 7

To install MongoDB 4.0 (for other versions, see release note) on CentOS 7, create file

vi /etc/yum.repos.d/mongodb-org-4.0.repo

Add content

[mongodb-org-4.0]
name=MongoDB Repository
baseurl=https://repo.mongodb.org/yum/redhat/$releasever/mongodb-org/4.0/x86_64/
gpgcheck=1
enabled=1
gpgkey=https://www.mongodb.org/static/pgp/server-4.0.asc

Install MongoDB with

yum install -y mongodb-org

Enable MongoDB start on boot

systemctl enable mongod

Start Mongo DB with

systemctl start mongod

To see mongoDB version, run

[root@ns3084948 ~]# mongo --version
MongoDB shell version v4.0.10
git version: c389e7f69f637f7a1ac3cc9fae843b635f20b766
OpenSSL version: OpenSSL 1.0.1e-fips 11 Feb 2013
allocator: tcmalloc
modules: none
build environment:
    distmod: rhel70
    distarch: x86_64
    target_arch: x86_64
[root@ns3084948 ~]#

To see if mongoDB running

[root@ns3084948 ~]# netstat -lntp | grep mongo
tcp        0      0 127.0.0.1:27017         0.0.0.0:*               LISTEN      10349/mongod        
[root@ns3084948 ~]#

Or use

[root@ns3084948 ~]# systemctl status mongod
● mongod.service - MongoDB Database Server
   Loaded: loaded (/usr/lib/systemd/system/mongod.service; enabled; vendor preset: disabled)
   Active: active (running) since Tue 2019-06-04 06:08:01 BST; 18min ago
     Docs: https://docs.mongodb.org/manual
  Process: 10347 ExecStart=/usr/bin/mongod $OPTIONS (code=exited, status=0/SUCCESS)
  Process: 10344 ExecStartPre=/usr/bin/chmod 0755 /var/run/mongodb (code=exited, status=0/SUCCESS)
  Process: 10341 ExecStartPre=/usr/bin/chown mongod:mongod /var/run/mongodb (code=exited, status=0/SUCCESS)
  Process: 10338 ExecStartPre=/usr/bin/mkdir -p /var/run/mongodb (code=exited, status=0/SUCCESS)
 Main PID: 10349 (mongod)
   Memory: 46.7M
   CGroup: /system.slice/mongod.service
           └─10349 /usr/bin/mongod -f /etc/mongod.conf

Jun 04 06:07:57 ns3084948.ip-145-239-4.eu systemd[1]: Starting MongoDB Database Server...
Jun 04 06:07:58 ns3084948.ip-145-239-4.eu mongod[10347]: 2019-06-04T06:07:58.013+0100 I CONTROL  [main] WARNING: Cannot detect if NUMA interleaving is enabled. Failed to probe "/sys/devices...ssion denied
Jun 04 06:07:58 ns3084948.ip-145-239-4.eu mongod[10347]: about to fork child process, waiting until server is ready for connections.
Jun 04 06:07:58 ns3084948.ip-145-239-4.eu mongod[10347]: forked process: 10349
Jun 04 06:08:01 ns3084948.ip-145-239-4.eu mongod[10347]: child process started successfully, parent exiting
Jun 04 06:08:01 ns3084948.ip-145-239-4.eu systemd[1]: Started MongoDB Database Server.
Hint: Some lines were ellipsized, use -l to show in full.
[root@ns3084948 ~]#

June 4, 2019

List SSH keys
To list all SSH keys used by ssh agent on your system, run
```
ssh-add -l
```
Example

To add all available ssh keys to agent, run
```
ssh-add
```
Remove SSH Key

To remove all SSH keys from agent, run
```
ssh-add -D
```
To remove specific key, run
```
ssh-add -d /path/to/file
```
Or you can just remove they ssh key files from your ~/.ssh folder.
May 29, 2019
SSH Agent forwarding with tmux
Most of the time i connect to remote virtial machine to SSH to other servers. This way i will always have a fixed IP, so i can white list my IP in firewall. I use tmux on this server, so even if i get disconnected, my connection to these servers won’t get disconnected. This is useful when you running some commands that take long to finish.

On this VPS, i don’t keep my SSH keys for security reason, instead i use SSH Agent forwarding with ssh -A option. From my PC, i connect to sshbox with command
```
ssh -A root@IP_OF_VM
```
If i start a new tmux session, i will be able to login to other servers using my SSH key. If i attach to pre extsing tmux session, my SSH key won’t work. This is because SSH Agent use an environment variable SSH_AUTH_SOCK, this point to a sock file. When you get disconnected, it get deleted.

To fix this problem, edit ~/.tmux.conf file
```
vi ~/.tmux.conf
```
Add
```
set-environment -g 'SSH_AUTH_SOCK' ~/.ssh/ssh_auth_sock
```
Create file
```
vi ~/.ssh/rc
```
with following content
```
if [ ! -S ~/.ssh/ssh_auth_sock ] && [ -S "$SSH_AUTH_SOCK" ]; then
    ln -sf $SSH_AUTH_SOCK ~/.ssh/ssh_auth_sock
fi
```
~/.ssh/rc file get executed every time a user connect using SSH. It will set symlink to SSH_AUTH_SOCK location if SSH agent forwarding is enabled.
May 28, 2019
List all files in an rpm package
To list all files in an rpm package run
```
rpm -ql PACKAGE_NAME
```
May 28, 2019

Category: Linux

Settings Password

Allow remote access

Download folder

Web interface

Method 2

Remove SSH Key