Category: Linux

atop
The program atop is an interactive monitor to view the load on a Linux system.

To install on Ubuntu/Debian
```
apt-get install atop
```
On CentOS/RHEL
```
yum install atop
```
On CentOS, you will need epel repo enabled.

atop commands

p – show process by cpu usage
d – show process by disk io usage
m – show process by memory usage.

View Historical Data

One of the powerful features of atop is its ability to record and store detailed snapshots of system performance, allowing you to go back and review exactly how resources were used at any given time. This is invaluable for diagnosing past performance issues, investigating system load patterns, and understanding resource usage over time. With atop’s logging capabilities, you can access historical data quickly and analyze it interactively, just as if you were viewing real-time activity.

Atop stores its log files by default in the /var/log/atop/ directory, with filenames that include the date (formatted as atop_YYYYMMDD), making it easy to locate and access historical performance data for specific days.

To view past data with atop, use the replay mode by running the following command:
```
atop -r
```
This will open today’s log file in replay mode. If you need older logs, you can specify the log file with -r option.
```
atop -r /var/log/atop/atop_YYYYMMDD
```
Replace YYYYMMDD with the desired date to load the log file for that day.

Once in replay mode, you can navigate through the data using keyboard shortcuts t and T to jump forward or backward in 10-minute intervals, and b or e to jump to the beginning or end of the log. This lets you explore historical resource usage interactively, just as you would with real-time data.

Back to Linux Commands
August 27, 2019
Using apt-get to manage software
apt-get used to manage packages in Debian/Ubuntu server.

Install A Package
```
apt-get install PKG_NAME
```
Uninstall a software (keep configuration file)
```
apt-get remove PKG_NAME
```
Uninstall a software and its configuration files
```
apt-get --purge remove PKG_NAME
```
To upgrade a software
```
apt-get upgrade PKG_NAME
```
Update Package Info
```
apt-get update
```
Remove Unwanted Programs
```
apt-get autoremove
```
Back to apt
August 27, 2019
install ShadowSocks client in Ubuntu 18.04
ShadowSocks client is part of shadowsocks package. This include both client and server. If you are looking to install server, see Install ShadowSocks server on Debian 10

To install ShadowSocks, run
```
apt install -y shadowsocks
```
ShadowSocks client is called sslocal, get installed in /usr/bin/sslocal.

On Ubuntu, no start up script provided with this package, so you need to create one or manually run sslocal when required.

Create a service file
```
vi /lib/systemd/system/shadowsocks-local@.service
```
Add following content
```
[Unit]
Description=Shadowsocks client mode service
Documentation=man:sslocal(1)
After=network-online.target

[Service]
Type=simple
User=nobody
Group=nogroup
ExecStart=/usr/bin/sslocal -q -c /etc/shadowsocks/%i.json
Restart=on-failure
RestartSec=30

[Install]
WantedBy=multi-user.target
```
Now we need to create a configuration file with your ShadowSocks server IP and password.
```
mkdir /etc/shadowsocks/
vi /etc/shadowsocks/local.json
```
Add following content
```
{
    "server":"YOUR_SERVER_IP",
    "server_port":8044,
    "local_address": "127.0.0.1",
    "local_port":8044,
    "password":"PASSWORD",
    "timeout":300,
    "method":"aes-256-cfb",
    "fast_open": false,
    "workers": 1,
    "prefer_ipv6": false
}
```
“server” = IP of the server where you installled ShadowSocks server.
“server_port” = Port used by ShadowSocks server
“password” = ShadowSocks server password.

local_port can be anything you like.

Enable shadowsocks service
```
systemctl enable shadowsocks-local@local
```
To start
```
systemctl start shadowsocks-local@local
```
To see status
```
systemctl status shadowsocks-local@local
```
Now you can configure your browser or other sock proxy supported application using 127.0.0.1:8044. Here is how to configure firefox
August 26, 2019

Install ShadowSocks server on Debian 10

To install ShadowSocks server on Debian 10, run

apt install -y shadowsocks

Create config file

vi /etc/shadowsocks/config.json

Add following

{
    "server":"SERVER_IP",
    "server_port":8044,
    "local_port":0,
    "password":"PASSWOARD_HERE",
    "timeout":600,
    "method":"aes-256-cfb"
}

You can change server_port if required.

To enable service, run

systemctl enable shadowsocks-server@config

To start shadowsocks proxy, run

systemctl start shadowsocks-server@config

For status/restart

systemctl status shadowsocks-server@config
systemctl restart shadowsocks-server@config

August 25, 2019

Install nslookup on ArchLinux
To install nslookup on ArchLinux, run
```
pacman -S dnsutils
```
August 20, 2019
Setting up MineCraft Server in Ubuntu
To setup MineCraft server on Ubuntu, first you need to install Java.
```
apt install openjdk-8-jre -y
```
Create a user to run minecraft
```
useradd -m --shell /bin/bash minecraft
```
You can set a password if you want direct SSH login to this user or login as root, then “su – minecraft”.
```
passwd minecraft
```
Login as user minecraft with SSH or “su”.

Download minecraft server .jar file from

https://www.minecraft.net/en-us/download/server/

At the time of writing, i downloaded
```
wget https://launcher.mojang.com/v1/objects/3dc3d84a581f14691199cf6831b71ed1296a9fdf/server.jar
```
Don’t use above link as it can get older, always go to minecraft site and get new link, so you get latest minecraft server jar file.

You can start minecraft server with command
```
java -Xmx1024M -Xms1024M -jar server.jar nogui
```
First time when you run, it exit with some error related to EULA.

You need to edit file
```
vi eula.txt
```
Set
```
eula=true
```
Now minecraft will run. You can create a run.sh file with following command for starting minecrat easily.
```
vi ~/start.sh
```
Paste following content
```
#!/bin/bash

java -Xmx1024M -Xms1024M -jar server.jar nogui
```
To make the file executable, chmod it 755
```
chmod 755 ~/start.sh
```
When you start minecraft from terminal/ssh, it get closed when you disconnect. To keep minecraft server running after you disconnect, use tmux or screen.
August 20, 2019
networking
On Ubuntu 19.04, networking service is provided by package ifupdown
```
apt install -y ifupdown
```
By default this package is not installed. So if you add network interface configuration in /etc/network/interfaces, it won’t work.

Ubuntu 18.04 + use netplan instead of ifupdown/networking service to configure network interfaces.

Linux KVM Bridge network on Ubuntu

Configure OVH Bridge Network from command line
August 18, 2019

Ubuntu Configure systemd-resolved

Latest Ubuntu/Debian use systemd-resolved for DNS resolution. On a fresh Ubuntu 19.04 install DNS failed to resolve.

root@ubuntu19:/# ping serverok.in
ping: serverok.in: Temporary failure in name resolution
root@ubuntu19:/#

To fix this, create file

mkdir /etc/systemd/resolved.conf.d/
vi /etc/systemd/resolved.conf.d/dns_servers.conf

Add content

[Resolve]
DNS=8.8.8.8 1.1.1.1

Restart systemd-resolved

systemctl restart systemd-resolved

You can find systemd-resolvd status with command

resolvectl status
systemd-resolve --status

To resolve a domain, use

resolvectl query serverok.in

August 18, 2019

Configure OVH Bridge Network from command line
If you have a Proxmox or VmWare ESXi server on OVH network, you need to configure network interface once virtual machine is created.

First login to OVH, go to IP page. Find the IP address you need to assign to this new VM, create a Virtual MAC. OVH allow 2 type of MAC. If you are using Proxmox, use OVH Mac. For VMWare ESXi, use vmware vmac.

Once you have Virual Mac. you need to configure it in your VM network interface settings. For Vmware ESXi

Now login to Virtial Machine, run following commands
```
ip link set NETWORK_INTERFACE_HERE up
ip addr add FO_IP_HERE dev NETWORK_INTERFACE_HERE
ip route add GW_IP_HERE dev NETWORK_INTERFACE_HERE
ip route add default via GW_IP_HERE dev NETWORK_INTERFACE_HERE
```
In above, replace

NETWORK_INTERFACE_HERE = name of your network interface. This can be found with command “ip link”. Normally it is eth0 or ensXXX.

FO_IP_HERE = this is the Failover IP you will be using for this Virtual Machine.

GW_IP_HERE = This is gateway IP. For OVH network, it will be your servers MAIN IP address with last number replaced with 254.

Here is an actial example.
```
ip link set ens192 up
ip addr add 178.33.35.183 dev ens192
ip route add 149.202.199.254 dev ens192
ip route add default via 149.202.199.254 dev ens192
```
This settings will be lost when you reboot OS. For configuring network interface permanantly, you can do
August 18, 2019

Install iperf3 on ArchLinux

To install iperf3 on ArchLinux, run

pacman -S iperf3

To do speed test

[root@tvmovies1 ~]# iperf3 -c ping.online.net -p 5209
Connecting to host ping.online.net, port 5209
[  5] local 163.172.50.206 port 50430 connected to 62.210.18.40 port 5209
[ ID] Interval           Transfer     Bitrate         Retr  Cwnd
[  5]   0.00-1.00   sec   282 MBytes  2.36 Gbits/sec    0    720 KBytes       
[  5]   1.00-2.00   sec   280 MBytes  2.35 Gbits/sec    0    755 KBytes       
[  5]   2.00-3.00   sec   281 MBytes  2.36 Gbits/sec   11    755 KBytes       
[  5]   3.00-4.00   sec   280 MBytes  2.35 Gbits/sec    0    758 KBytes       
[  5]   4.00-5.00   sec   281 MBytes  2.36 Gbits/sec    0    758 KBytes       
[  5]   5.00-6.00   sec   256 MBytes  2.15 Gbits/sec  1507   42.4 KBytes       
[  5]   6.00-7.00   sec   115 MBytes   965 Mbits/sec  6917    130 KBytes       
[  5]   7.00-8.00   sec   114 MBytes   954 Mbits/sec  6643   48.1 KBytes       
[  5]   8.00-9.00   sec   114 MBytes   954 Mbits/sec  6749    119 KBytes       
[  5]   9.00-10.00  sec   112 MBytes   944 Mbits/sec  6923   38.2 KBytes       
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval           Transfer     Bitrate         Retr
[  5]   0.00-10.00  sec  2.07 GBytes  1.77 Gbits/sec  28750             sender
[  5]   0.00-10.00  sec  2.06 GBytes  1.77 Gbits/sec                  receiver

iperf Done.
[root@tvmovies1 ~]#

Here we do speed test with http://ping.online.net, they run iperf3 server on port 5209

August 17, 2019

Install netdata on ArchLinux
First update the packages with
```
pacman -Syu
```
Install netdata
```
pacman -S netdata
```
Enable and start netdata
```
systemctl enable netdata
systemctl start netdata
```
August 17, 2019
Ubuntu remove SSH welcome message
When you login to an Ubuntu server using SSH, you get welcome message like

On most Linux systems, this is generated by /etc/motd. On Ubuntu, MOTD (message of the day) generated dynamically with some scripts. I don’t want to see all the marketing message from Ubuntu everyday.

To disable MOTD on Ubuntu, just delete the scripts from /etc/update-motd.d/
```
rm -f /etc/update-motd.d/*
```
If you want a differnt motd, you can put a shell script in this folder.

Method 2

Another way to disable motd is by disabling pam_motd.so module.

Edit files
```
/etc/pam.d/login
/etc/pam.d/sshd
```
Comment out the lines related to pam_motd.so
```
session    optional     pam_motd.so  motd=/run/motd.dynamic
session    optional     pam_motd.so noupdate
```
August 17, 2019

Category: Linux

atop commands

View Historical Data

Method 2