bookmark_borderHow To List UFW Rules When The Application is Inactive or Disabled

When working on your server you might need to disable the Uncomplicated Firewall (UFW). When doing so you’ll notice it doesn’t display your rules when the application is inactive.

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bookmark_borderHow to Auto-Update CentOS 7 Packages with Yum-Cron

If you’re looking for a quick way to keep your CentOS machine patched at all times, become friends with yum-cron.

To install, in terminal, use:

#yum -y install yum-cron

The -y forces the install, answering any Yes / No “are you sure” questions.

Once installed, be sure to start the service using:

# systemctl start yum-cron.service

You can verify the status (make sure it’s running) using:

# systemctl status yum-cron.service

Output should look something like:

yum-cron.service – Run automatic yum updates as a cron job
Loaded: loaded (/usr/lib/systemd/system/yum-cron.service; enabled; vendor preset: disabled)
Active: active (exited) since Mon 2016-11-07 19:16:01 UTC; 2s ago
Process: 5385 ExecStart=/bin/touch /var/lock/subsys/yum-cron (code=exited, status=0/SUCCESS)
Main PID: 5385 (code=exited, status=0/SUCCESS)

Last step is to make sure it’s enabled, this will make sure it restarts in the event the machines reboots later.

# systemctl enable yum-cron.service

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bookmark_borderHow do you add color or bold the echo outputs in a shell script?

If you’re working in linux you will be introduced to writing shell scripts at some point. When you do, you’ll become very familiar with the echo.

If you open your terminal, and run an echo command it’ll literally echo whatever you put after the echo:

$ echo "Hello World" Hello World
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bookmark_borderTar (Compress) a Directory without Images via Terminal

Sometimes you need to compress an entire directory, but sometimes you want to ignore specific file types.

Here is a basic command that you can use to remove specific file types before you compress it. In this example we use the find command to look for, and ignore, all image file types. That then gets piped into the tar command:

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bookmark_borderHow do you enable SFTP on your Ubuntu server?

SFTP is a file transfer protocol. It wraps the File Transfer Protocol (FTP) inside the Secure Shell (SSH) protocol. This allows the communication to be protected as it moves from one point to another.

PSA: Using FTP is considered an insecure transfer protocol and should be avoided.

This article assumes you are trying to create new SFTP users on your linux machine. In this example we’ll be using Ubuntu 18.04.

Enabling and Creating SFTP users:

To enable SFTP you have to enable it inside your SSH configuration file. It’s often located here: /etc/ssh/sshd_config. Open the file and add the following to the end of the configuration file:

# override default of no subsystems
Subsystem       sftp    /usr/lib/openssh/sftp-server
Match group sftp
X11Forwarding no
AllowTCPForwarding no
ForceCommand internal-sftp

Options explained:

OptionDescription
SubsystemAn abstraction layer that allows you to invoke remote commands. In this instance, we’re invoking sftp-server.
MatchAllows you to limit actions in shell, in this instance we’re limiting the actions to a specific group – sftp. Only those users inside the SFTP group will be able to SFTP into the server.
X11ForwardingThis is a special case for remote tunneling. Unfortuantely it can be used maliciously by a bad actor, so it’s recommended your disable unless you know what you’re doing.
AllowTCPForwarding“TCP Forwarding” allows you to encapsulate any other protocol (based on TCP of course) inside an already established SSH connection. There are a lot of reasons for this, but we don’t want to allow SFTP users to use this without appropriate planning.
ForceCommandThe remote system can only execute a set of statically defined commands. Specifying a command of internal-sftp will force the use of an in-process SFTP server that requires no support files when used with ChrootDirectory.

Once you add this to the SSH config file you need to restart OpenSSH:

service ssh restart

Now you need to add new SFTP users, and apply the user to the right group.

useradd -m [newsftpuser] -g sftp

Set the password:

passwd [newsftpuser]

Now you can test your SFTP connection, from a different server:

sftp [newsftpuser]@[serverIPaddress]

Happy SFTP’ing!

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bookmark_borderCan you move files types from one location to another in linux?

There are instances where you want to quickly locate and move specific file types from point A to Point B.

Example:

Move all PHP files from /home/$user/php-files/ to /home/$user/php-mv-files

Easiest way to do this is to use the Find command in terminal.

$ find ./ -name "*.php"

./php-files/file3.php
./php-files/file2.php
./php-files/file1.php

This lists all the PHP files in the /php-files directory.

To move the files, you run the following command:

$ find ./php-files/ -name "*.php" -exec mv {} ./php-mv-files/ \;

This will move all files from ./php-files to ./php-vmv-files. Running the original Find command will get you the following:

$ find ./ -name "*.php"
./php-mv-files/file3.php
./php-mv-files/file2.php
./php-mv-files/file1.php

In this instance, -exec mv {} says, run the MV command on the files selected from the original find, that’s what the {} implies. You then escape, and close the command using \;. This final piece is critical to stopping the command.

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bookmark_borderHow do you add something to the Path environmental variable?

Path environmental variables are variables that function like a shortcut for your system. They allow you to define directories where executables are located.

Assume you installed this application picc-9.82.9453-linux.run. Without setting the path you’d have to run this every time in your terminal:

# /usr/hitech/picc/9.82/bin/picc

Instead of:

# picc

Running picc without having to define the path every time is so much easier, and faster. To achieve this experience you have to add the application executable to the Path environmental variable.

The first option is edit your user profile:

$ vim ~/.bash_profile

It will look something like this:

# .bash_profile

# Get the aliases and functions
if [ -f ~/.bashrc ]; then
. ~/.bashrc
fi

# User specific environment and startup programs

PATH=$PATH:$HOME/bin

export PATH

You are looking to edit this section:

PATH=$PATH:$HOME/bin

Update the path with new application location (e.g., /usr/hitech/picc/9.82/bin) using the colon (:) as the separator.

PATH="$HOME/bin:$PATH:/usr/hitech/picc/9.82/bin"

Save the file, and try running the command in your terminal.

# picc

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bookmark_borderHow to set recurring job in Linux using Cron jobs?

Whenever you’re working with linux you’ll find yourself in need of running tasks repeatedly. The easiest way to do this is to set up a recurring job using Cron.

crontab file contains instructions for the cron(8) daemon in the following simplified manner: “run this command at this time on this
date”. – Cron Man Page

You can edit your cron jobs using crontab, specifically:

# crontab -e

If you have any other cron jobs you’ll see other entries. If not, you’ll be able to create your own entries using your favorite editor (e.g., VIM, Nano, VI, etc…).

The format for a cron entry is as follows:

minute hour day-of-month month day-of-week command

There is a great tutorial available here: https://crontab.guru/every-1-hour

If I want to run a job every hour, this is the entry I’d add to Cron:

0 * * * * cd /root/scripts && ./checkrunningprocess.sh

If you ever want to see what jobs you have running you can run:

crontab -l

and you’d see something like this:

# crontab -l
0 * * * * cd /root/scripts && ./checkrunningprocess.sh

Happy automating!

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bookmark_borderHow do you add a user to a new group in linux? Something like Sudoers, Apache, or something else…

When you’re working with linux you might have to add a user to different group.

Let’s say that you want to create user John, and you want John to have root abilities. To do this you’re going to want to add the user, John, to the sudoers group.

The sudoers group controls who has Sudo privileges on a machine. Sudo is a command that allows a user to run commands based on another users privileges, in most instances it is configured to run as root. Fun fact, SUDO was established from “superuser do.”

To add user John to the sudoers group you would do something like this:

# usermod -aG sudoers John

The two options used include:

  • a – Add the user to the supplementary group(s). Use only with the -G option.
  • G – A list of supplementary groups which the user is also a member of. Each group is separated from the next by a comma, with no intervening whitespace.

You have to use both options in conjunction with each other. You can find a more detailed list of options here: https://linux.die.net/man/8/usermod

This same model applies to any group and can be used for any user. A great example is Apache on a web server. 🙂

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bookmark_borderHow do I find all files containing specific text on Linux?

If you are looking for specific content but can’t remember where it’s located on the server, this post is for you. It will show you how to find specific text anywhere in a folder, or server.

We are going to use the GREP command when doing searches in linux.

grep searches input files for lines containing a match to a given pattern list. When it finds a match in a line, it copies the line to standard output (by default), or produces whatever other sort of output you have requested with options.

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