Check laptop battery percentage using terminal

There are 2 methods to do this.

First method

The first method is to use cat to display the content of /sys/class/power_supply/BAT*/capacity 

$ cat /sys/class/power_supply/BAT*/capacity

To see the updated value, refreshed every second. -n1 is for refresh every second, and -d is to highlight any changes.

$ watch -n1 -d 'cat /sys/class/power_supply/BAT*/capacity'

Second method

The second method, is to use upower command. To use this command, you need to know the object paths available for your device

$ upower -e

/org/freedesktop/UPower/devices/line_power_AC

/org/freedesktop/UPower/devices/battery_BAT0

/org/freedesktop/UPower/devices/battery_BAT1

/org/freedesktop/UPower/devices/DisplayDevice

So, to check the my first battery information, use below command

$ upower -i /org/freedesktop/UPower/devices/battery_BAT0 | grep percentage

Same goes with the second battery

$ upower -i /org/freedesktop/UPower/devices/battery_BAT0 | grep percentage

Using putty via cmd

Putty is an ssh client that many windows users used to connect to ssh server. Due to the complexity of ssh protocol, the settings in putty is also quite complex. 

Here I want to show some examples where you can use putty via the cmd. You can simply copy below commands and paste it inside your cmd, do some changes like IP, username and port, and you are good to go without having to go through many steps to complete some simple task such as setting up a dynamic tunnel.

The first thing that you have to do before using putty via cmd is, to install putty. Just download the installer from here, and install it using the usual double click on installer method.

Once installed, fire up your cmd. 

Below are some basic scenario to use putty (if you are familiar with the linux openssh client, the options are almost identical)

Scenario 1: Connecting to a remote server (with ip 10.10.10.10):

cmd> putty user@10.10.10.10

Scenario 2: Forward a remote port to you local machine, in this case, forwarding port 22 on 10.10.10.10 to port 9999 on your local machine

cmd> putty user@10.10.10.10 -L 9999:localhost:22

Scenario 3: Forward a local port to a remote machine, in this case, forwarding port 22 in localhost to 9999 in remote machine

cmd > putty -R 9999:localhost:22 root@10.0.0.16

Scenario 4: Create a socks5 proxy (dynamic tunnel) on port 8888 in localhost via the remote machine. This is useful if we want to browse addresses that only can be accessed by the remote machine, but the remote machine does not have an internet browser.

cmd> putty user@10.10.10.10 -D 8888

Scenario 5: Connect to a remote machine, via port other than 22. In this case, sshd is running on port 9999

cmd> putty -P 9999 user@10.10.10.10

There you go, 5 scenarios where you can use putty via command line. Hope this will make your life easier when using putty. Ciao!

Checking your public IP from terminal

Sometimes, when you are setting up a linux machine, there is a need to know what IP our machine is being connected to the public internet. There are many websites that provide this kind of service, but below are some of my favorites that work well with commands. 

To be able to use this, we need a text based web browser. We will use curl in this case. Install curl if your machine does not have one.

# yum install curl -y

To get our ip address, run curl like below. Choose whichever you like :).

$ curl ipecho.net/plain

210.210.210.210

$ curl icanhazip.com

210.210.210.210

The best, in my opinion is ipinfo.io, because it will give you a nicely formatted information regarding your public IP address, and if you want a specific info, just put it as a slash being ipinfo.io. For example, if you want to know what is your city, just curl ipinfo.io/city

$ curl ipinfo.io

{

  "ip": "210.210.210.210",

  "city": "Kuala Lumpur",

  "region": "Kuala Lumpur",

  "country": "MY",

  "loc": "3.1390,101.6869",

  "org": "AS4818 Digi Telecommunications Sdn. Bhd.",

  "postal": "50505",

  "timezone": "Asia/Kuala_Lumpur",

  "readme": "https://ipinfo.io/missingauth"

}

$ curl ipinfo.io/ip

210.210.210.210

$ curl ipinfo.io/city

Kuala_Lumpur

Simple http/https proxy using squid

This is a basic proxy setup, whereby you practically does not have to do any settings.

First, install squid in our machine with address 10.0.0.10

# yum install squid -y

Then, start squid service

# systemctl start squid

By default squid runs on port, 3128, so we will allow 3128/tcp on our firewall

# firewall-cmd --add-port 3128/tcp

# firewall-cmd --add-port 3128/tcp --permanent

Now the time to test out our proxy, in a different machine. This test machine does not have any internet connection to the outside world, except network connection to our proxy server.

First we use curl to try to reach ipecho.net/plain without proxy

$ curl ipecho.net/plain

curl: (6) Could not resolve host: ipecho.net

Next we will use curl with our brand new proxy. We can see that our machine is able to reach ipecho.net/plain, with the help of the proxy.

$ curl --proxy http://10.0.0.10:3128 ipecho.net/plain

210.210.210.210

Nice, happy proxying.

Set static IP address in ubuntu 18.04

Starting from ubuntu 18.04, network configuration is now handled by netplan, which is based on YAML.

To set a static ip in netplan, you need to know what is the interface name that you want to configure. To do that, just run "ip address" command

$ ip address

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000

    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00

    inet 127.0.0.1/8 scope host lo

       valid_lft forever preferred_lft forever

    inet6 ::1/128 scope host 

       valid_lft forever preferred_lft forever

2: enp0s3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000

    link/ether 08:00:27:18:46:ea brd ff:ff:ff:ff:ff:ff

    inet 192.168.0.154/24 brd 192.168.0.255 scope global dynamic enp0s3

       valid_lft 604595sec preferred_lft 604595sec

    inet6 2001:e68:542c:e410:a00:27ff:fe18:46ea/64 scope global dynamic mngtmpaddr noprefixroute 

       valid_lft 259188sec preferred_lft 172788sec

    inet6 fe80::a00:27ff:fe18:46ea/64 scope link 

       valid_lft forever preferred_lft forever

3: enp0s8: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN group default qlen 1000

    link/ether 08:00:27:7d:fa:68 brd ff:ff:ff:ff:ff:ff

You can see that we have 2 interfaces, enp0s3 and enp0s8. Now we have to locate which file need to be edited to give enp0s8 a static IP address. We can do that by:

$ ls /etc/netplan/

01-netcfg.yaml

To add an ip address  of 10.10.10.10/24 to enp0s8, with gateway 10.10.10.1 and nameserver 8.8.8.8 and 8.8.4.4, simply edit /etc/netplan/01-netcfg.yaml as per below

$ sudo vi /etc/netplan/01-netcfg.yaml

network:

  version: 2

  renderer: networkd

  ethernets:

    enp0s3:

      dhcp4: yes

    enp0s8

      dhcp4: no

      addresses: [10.10.10.10/24]

      gateway4: 10.10.10.1

      nameservers:

        addresses: [8.8.8.8,8.8.4.4]

Save the file. Since this is a yaml based configuration, make sure that the indentation is uniform across the file. To test your configuration for any syntax error, and press ENTER if you agree to use the configuration:

$ sudo netplan try

Do you want to keep these settings?

Press ENTER before the timeout to accept the new configuration

Changes will revert in 119 seconds

Configuration accepted.  

Once accepted, verify the ip has been set using "ip address" and "ip route"

$ ip address show dev enp0s8

3: enp0s8: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000

    link/ether 08:00:27:7d:fa:68 brd ff:ff:ff:ff:ff:ff

    inet 10.10.10.10/24 brd 10.10.10.255 scope global enp0s8

       valid_lft forever preferred_lft forever

    inet6 fe80::a00:27ff:fe7d:fa68/64 scope link 

       valid_lft forever preferred_lft forever

$ ip route show dev enp0s8

default via 10.10.10.1 proto static 

10.10.10.0/24 proto kernel scope link src 10.10.10.10 

Using rsync without ssh

Recently I have encountered a situation whereby I need to transfer a file to a server, and ssh client and server are not installed in that server. And to make matters worst, that server does not have internet connection for me to install openssh-clients on it. Luckily, that server has rsync installed, which kind of save my day. 

What I will show here, is how to transfer file using rsync protocol without ssh. We will call the server without ssh, and without internet connectivity with serverA, and the other server that has internet connectivity as serverB.

serverA: server without ssh and internet connectivity

serverB: server with internet connectivity

After I have acquired all the files needed by serverA by downloading in serverB, I need to start rsync in daemon mode. Before that, I need to tell rsync which folder that I wish to share via the rsync protocol, by editing /etc/rsyncd.conf. Let's say I want to share my /tmp directory, which contain a file called myfile.txt.

serverB # cat >> /etc/rsyncd.conf <<EOF

[tmp]

    path = /tmp

EOF

Next, start rsync in daemon mode. Rsync will make use of the /etc/rsyncd.conf for the daemon configuration.

serverB # rsync --daemon

We can see that rsync by default will listen on port 873

serverB # ss -tulpn | grep rsync

tcp     LISTEN   0        128              0.0.0.0:873             0.0.0.0:* 

In serverA, we need to use the rsync command to connect to rsync daemon in serverB. To check which directory is available for download:

serverA # rsync serverB::

tmp

Download the file

serverA # rsync serverB::tmp/myfile.txt

serverA # ls 

myfile.txt

You have now downloaded the myfile.txt file, from serverB just by using rsync. A note to remember, rsync protocol does not have any encryption, but it is good enough for a LAN environment.

Download rpm installer file for already installed packages

If you have not install the packages, you can always use --downloadonly flag to just download the packages without installing. For example, I want to download rpm file for curl

# yum install --downloadonly curl

The file and its dependencies will be saved into /var/cache/yum.

But if you have installed the package, the above command will only return a message saying that "Packages is already installed, and nothing to do."

In order to download rpm file of an installed package with dependencies, another command is needed, which is repotrack, that is a command in yum-utils package.

First, install yum-utils

# yum install -y yum-utils

Then, run repotrack on the package that you need the rpm installer

# repotrack curl

All the packages will be downloaded to the current directory. Nice!

Minio on podman failed to run due to wrong selinux tag

 I tried to install minio on podman, following this guide.

I created a directory for data

# mkdir /data

I then start minio container

# podman run -dit -p 9000:9000 -e "MINIO_ACCESS_KEY=minioadmin" -e "MINIO_SECRET_KEY=myminioadmin" -v /data:/data  minio/minio server /data

The container was started, but exited as soon as it finished starting up

# podman ps

CONTAINER ID  IMAGE                         COMMAND       CREATED        STATUS            PORTS                   NAMES

# podman ps -a

CONTAINER ID  IMAGE                         COMMAND       CREATED        STATUS            PORTS                   NAMES

fb7073bc3baf  docker.io/minio/minio:latest  server /data  6 minutes ago  Exited (1) 6 minutes ago   0.0.0.0:9000->9000/tcp  wonderful_galois

Checking the log, I found out that the container failed to start due to permission error on the /data

# podman logs fb 

The error is as in below image

I checked the directory, but the permission is correct

# ls -ld /data

drwxr-xr-x. 3 root root 24 Nov  4 03:55 /data

This must be selinux. So I searched around for a proper tag for minio related files and directories. Referring to this article, I decided to use the tag for content as per that article.

# chcon -R system_u:object_r:container_file_t:s0 /data

Now, time to test. I rerun the container.

# podman start fb

# podman ps

CONTAINER ID  IMAGE                         COMMAND       CREATED         STATUS            PORTS                   NAMES

fb7073bc3baf  docker.io/minio/minio:latest  server /data  14 minutes ago  Up 2 seconds ago  0.0.0.0:9000->9000/tcp  wonderful_galois

Yes, it worked. If you guys ever encounter the permission issue, make sure to check the selinux tag, besides checking the standard unix permission on the directory.