Saturday, May 8, 2021

Listing docker containers according to fields

Command like 'docker ps' is a good tool to check on your running container/s. This is visually pleasant if you do not have many containers. What if you have hundreds of containers, and you just want to print just the names of the containers, or even better the names and id of the containers?

We can use --format flag in this situation. This flag is available on pretty much every docker commands that produce some kind of output to stdout, so that you can filter what you want to see as the output.

To use this flag, you just need to follow below format:
$ docker ps --format '{{json .Names}}'


whereby ".Name" is the field that you want to be displayed. For example, you want to list out just the ID of all the running containers, you can use:
$ docker ps --format '{{json .ID}}'


You can see that the field is different from the displayed field name without the --format flag.
$ docker ps
e914bd4963d4   alpine    "/bin/sh"   29 minutes ago   Up 29 minutes             hardcore_carson

To know which flag is available to be used:
$ docker ps --format '{{json .}}'

{"Command":"\"/bin/sh\"","CreatedAt":"2021-05-08 11:32:12 +0800 +08","ID":"e914bd4963d4","Image":"alpine","Labels":"","LocalVolumes":"0","Mounts":"","Names":"hardcore_carson","Networks":"bridge","Ports":"","RunningFor":"33 minutes ago","Size":"0B (virtual 5.61MB)","State":"running","Status":"Up 33 minutes"} 

To list 2 (or more) fields:
$ docker ps --format '{{json .ID}} {{json .Names}}'

"e914bd4963d4" "hardcore_carson" 

You can also use the --format without the json keyword, the only different is the output would not be double quoted (which is not easy on the eyes if you have many fields)

$ docker ps --format '{{.ID}} {{.Names}}'

e914bd4963d4 hardcore_carson


Thursday, April 29, 2021

Checking if our password is based on a dictionary word on linux command line

There is a package in linux that can be used to check the our password, if it is based on a dictionary word, and that is libcrack (or libcrack2 in debian based).

To install the package:
  • In redhat family:
# yum install cracklib -y
  • In debian family:
# apt install libcrack2

To use, just run cat and pipe it against cracklib-check command, and supply your password after that. Do not forget to type ctrl-d or ctrl-c to get back to the shell, once done.
$ cat | cracklib-check


password: it is based on a dictionary word
$ cat | cracklib-check


Xeir3oongex*: OK

Thursday, April 22, 2021

Adding Rules to Firewalld before Starting It

This is really useful if we want to start firewalld via ssh. If we start firewalld without allowing ssh, we will be locked out from the machine.

The solution is, to use a command called firewall-offline-cmd. This tool acts similarly with firewal-cmd, except it works during the daemon is dead.

To avoid being locked out of a remotely accessed, we should first allow ssh in firewalld

$ sudo firewall-offline-cmd --add-service ssh

We are now safe to start firewalld

$ sudo systemctl start firewalld

Once started, we can make the rule permanent on firewalld restart 

$ sudo firewall-cmd --add-service ssh --permanent

Make firewalld start automatically on every server boot 

$ sudo systemctl enable firewalld

Wednesday, April 21, 2021

Changing Kernel on Next Boot

To choose which kernel version you want to boot into on next reboot, below are the steps

1. Check what kernel version is available

# grep ^menuentry /etc/grub.cfg

2. Choose which kernel that you want to boot from, remember that the list from the above command start from 0. Let's say we want to choose the second kernel

# grub2-set-default 1

3. Rebuild grub.cfg

# grub2-mkconfig -o /boot/grub2/grub.cfg

4. Reboot the server

# reboot 

You server will reboot to the kernel version that you choose above. 

Sunday, April 18, 2021

Running php-fpm and Nginx in Docker

Php-fpm is an advanced and highly efficient processor for php. In order for your php files to be viewable in a web browser, php-fpm needs to be coupled with a web server, such as nginx. In this tutorial we will show how to setup php-fpm and nginx is docker.

1. Create a directory for your files 

$ sudo mkdir phpfpm

2. Create a network for the containers to use. This makes sure that we can use container's name in the configuration file.

$ docker network create php-network

3. Create nginx config file

$ cd phpfpm

$ cat > default.conf <<EOF

server {

    listen  80;    

# this path MUST be exactly as docker-compose.fpm.volumes,

    # even if it doesn't exist in this dock.

    root /complex/path/to/files;

    location / {

        try_files $uri /index.php$is_args$args;


    location ~ ^/.+\.php(/|$) {

        fastcgi_pass fpm:9000;

        include fastcgi_params;

        fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name; 




4. Create an index.php file with some random php code (we are using phpinfo() to make it easier)

$ cat > index.php <<EOF

<?php phpinfo(); ?> 


5. Run a php-fpm container, in detached and intaractive mode, using php-network, and we mount /home/user/phpfpm to /var/www/html in container

$ docker run -dit --name fpm --network php-network -v /home/user/phpfpm:/var/www/html

6. Run an nginx container in detached and intaractive mode, using php-network, and we mount /home/user/phpfpm/default.conf to /etc/nginx/conf.d/default.conf in container

$ docker run -dit --name nginx --network php-network -v /home/user/phpfpm/default.conf:/etc/nginx/conf.d/default.conf -p 80:80 nginx

7. Open a browser, and browse to http://localhost, you should now be able to see the PHPinfo page. 

Of course, there is an easier way to set this up using docker-compose. We will cover that in another post.