Linux shell

Restart service on no linux logs output

Sometimes I have apps that suddenly stop working, however they don’t have PID output or I can’t start them via systemd or upstart due to convoluted requirements. Other times the app is on but it stops processing incoming queues due to various reasons. I need to make sure i have a mechanism in place to Restart service as needed. I’m going to describe how you can check for Linux logs output and if there is no log for X seconds then we restart the app! we check the log every X seconds and if in the past X seconds there is no movement we perform X function.

Restart service script

# simple script to check logs, if no entries have been made in 45 seconds restart
set -x

TS=$(date +%s)

timer1=$(expr $TS - $(date +%s -r /path/to/some/file.log)) # make sure to set the log path here

if [ "$timer1" -gt 45 ]
        echo $timer1
        echo "restarting service due to no activity for 45 seconds"
        sudo service mycoolservice restart    # you can change this for something else such as sending email or even rebooting the machine.
Linux shell

Ubuntu & Bash tutorial & basic utilities

An introduction to the CLI (Command Line Interface) and Bash on Ubuntu Linux aka a bash tutorial

The default shell that is installed on Ubuntu Linux is bash. Alternatives exist, but they’re beyond the scope of this tutorial (check our post here for more info on how to isntall a better alternative to bash called Zshell or zsh). Bash is available on almost all Linux distributions, so this tutorial will work on most Linux distributions as well.

What is a shell? Simply put, the shell is a program that takes your commands from the keyboard and gives them to the operating system to perform. In the old days, it was the only user interface available on a Unix computer. Nowadays, we have graphical user interfaces (GUIs) in addition to command line interfaces (CLIs) such as the shell. Bash is the most popular shell application for Linux, and is the default on Ubuntu and hundreds of other Linux distributions, Mac OS X, and soon Windows 10.

The basics are:

  • You type one or more command(s), hit enter, and it runs the command(s).
  • Use the up/down arrows to go through your bash history. Ctrl+P also works
  • Use Ctrl+R to search the history of commands used previously.
  • Hitting tab will autocomplete commands.

Instead of typing
cd ~/myfolder1/
you can just type
cd ~/my<tab>
and it’ll either autocomplete fully or if there are still more folders (like my234 and myfolder1), it’ll show you your options. You can enter multiple commands by separating them with “;” or “&&”. ; allows commands to run one after another, && runs next command only if first succeeds. For clarity, we will focus only on single commands.

Bash and Linux in general is case sensitive. That means you can have new_folder, New_folder, NEW_FOLDER, and new_Folder all in the same directory. If the computer says a file or folder doesn’t exist, you should check to see if you forgot to capitalize something. This is another good use of tab complete!

The gist of it is that a command takes in arguments/parameters, so you enter your command, add a space, add your arguments. An argument CANNOT HAVE SPACES. A space means that the argument is done and you’re putting in another argument. To circumvent this, you have two options:

  1. Escape all spaces by using a backslash (\). This is the foolproof method that will work every time. Tab autocomplete will put these in for you.
    cd My\ Really\ Annoying\ Folder\ Name
  2. Put the argument in quotations (Works 99% of the time)
    cd “My Really Annoying Folder Name”

Here are the basic things that you’ll need to know how to do to get around.

Commonly used commands

commandWhat it doesExamples
manWith man, you can retrieve the information in the manual about a command and display it as text output on your screenman ls,
page-up/down or arrow keys to browse, q to quit, / to search
lsLists all the files and folders in the current directory.

Commonly launched with arguments -lsah for better output formatting.

ls Documents
text.txtls -lsah Documents

total 3

  0 drwxr-xr-x+  76 username group   2.5K Apr 19 18:52 .

  0 drwxr-xr-x    6 root admin   204B Dec 24 01:01 ..

  8 -r——–    1 username group     7B Nov 10 20:41 text.txt

cdChanges directory. To go up a directory, its cd .. (two periods). cd with no parameters sends you to your home folder.

Using ~ will change you to your home directory and – will return to your previous working directory.

cd ..
cd my_folder
rmDeletes files. Will delete folders recursively too with the -r option.

The -f option will forcefully remove files without warning
Common meme is telling people to rm -rf /, DON’T !

rm my_file.txt
rm -r my_folderrm -rf my_folder #forcefully removes a directory and its contents
rm –no-preserve-root -rf / #This will recursively forcefully remove all files from your filesystem, don’t do it.
rmdirRemoves an empty directory (Note: Doesn’t work for non-empty directories)rmdir test #Removes test directory
cpCopies files and directories. Use -R for copying directories.cp my_file.txt my_file_copy.txt

cp my_file.txt directory/my_file.txt

cp -R my_folder my_folder_copy

mvMoves files and folders. Also the way to rename things in the command my_file.txt this_subdirectory/my_file.txt

mv my_old_foldername my_new_foldername

pwdPrints what folder you’re in. Sort of useful, but your shell should have the folder you’re in.pwd
!!Re run the last command.
This can be combined with other commands.


cd ..




sudoRuns a command as a different user, by default root. Does not work with cd.mkdir folder

mkdir: cannot create directory ‘folder’: Permission denied
sudo mkdir folder

(You will be asked for a password and the permission issues should go away)
sudo !!

[sudo] password for user:

(this does the same thing as above)

mkdirMakes a directorymkdir folder
chmodChanges file permissions (read, write, execute) + to add the permission to your user, – to remove.chmod +x myprogram
chmod -xchmod 777 filename.txt (Allow anyone to edit)
nanoThe easiest command line text editor. No arguments opens it just like opening notepad.exe without opening with a file.

Type ctrl+o to save, and ctrl+x to exit.

nano mytextfile.txt
passwdChange your password. (often has be run as root or be preceded by sudo )passwd

Changing password for <user>

(current) UNIX password:guest

Enter new UNIX password:hunter2

Retype new UNIX password:hunter2

catConcatenate two (or one) files or print everything in a file. Not recommended for viewing files, use less for that my_file.txt

<content of my_file.txt appears on screen>

headPrint the first 10 lines of a text file.head my_file.txt
tailPrint the last n lines of a text file. Super useful for log files.

If it is invoked with the argument -f it lets you continuously view the file in real time.

tail -n 10 -f logfile.txt
lessAllows you to view a text file without editing it.

Can also view log files using +F (similar to tail -f)

less my_file.txt

less +F logfile.txt

grepAllows you to use regular expressions to search through the output of a program or a file. Search for text in all files in a folder with the “-r” switch.grep ‘Error:’ my_file.txt
grep -r `find me’ my_directory/
tarExtract files from tar archives.

Common options:

tar -xzf : extract files from gzip compressed tar archive

tar -xjf : extract files from bzip2 compressed tar archive

tar -xzf system_backup_2016_04_07.tar.gz

Best way to remember tar -flags
Modern versions are smart enough to detect the format, so you can use -xf or -cf (eXtract File, Create File)

touchCreate an empty file with the specified name if the file does not exist.

Will also update the file date of an existing file without modifying the content

topTerminal-based GUI for viewing processestop
lnUsed for creating links (shortcuts) in the filesystem.
In general always use -snf (trust me)
ln -snf /opt/foo /usr/bin/bar
/usr/bin/bar now links to /opt/foo, and it is transparent to the operating system.
screenscreen let’s you run multiple login sessions in the same terminal. Say you want to run a process, you can launch it through screen, detach it, and then later come back to the same process.

When inside a screen session, type CTRL+A, then CTRL+D to detach it (put it into the background).
When you later want to reattach to the screen session, type screen -r. If you only have one screen session, you will be brought right back, otherwise you will have to specify the session id

screen bash

screen -r

screen -ls

There are screens on:

767.ttys000.localhost (Detached)

844.ttys002.localhost (Detached)

2 Sockets in /var/some/folder/random/T/.screen.

screen -r 767.ttys000.localhost

whoamiPrints the currently logged in user.whoami


whereisPrints the location of a command.whereis echo


whichPrints the location of a command.which echo


echoOutputs text to the command line. Useful when writing shell scripts.echo “hello world”

Hello world

killAttempt to terminate processkill (process id)

*if ineffective, try kill -15 or kill -9 if 15 does not work (kill -9 will forcibly terminate almost any process)

killallWill attempt to terminate a process. killall firefox
fileShows you the file typefile my_file.txt

my_file.txt: UTF-8 Unicode text

dateShow the current date in text formdate

Tue Apr 19 15:31:54 CDT 2016

psDisplay information about processes (different than top…) ps -ef
can also search for processes: ps -ef | grep firefox
aproposFind commands that do a given task, Will return a list of commands that have the searched parameter in their man file.
Note: similar functionality to running  “man -k command”.
apropos remove
Colrm (1) – remove colums from a fileCut () – remove sections from each line of files

apropos concat
cat (1)           – concatenate files and print on the standard output

cat (1p)          – concatenate and print files

eval (1p)         – construct command by concatenating arguments

aliasVery useful for creating custom shorcuts for commonly used programs or parametersalias lcolor=’ls –color=auto’
Now lcolor is the same as ls –color=autoBut shorter
envList environment variables / set environment variablesenv



The filesystem in a nutshell

“Everything is a file”. In Linux, everything is treated as a file, even your devices.

Unlike Windows and DOS, Unix systems and Linux do not have drive names. Your thumb drive will be mounted as a “folder” on Linux – Instead of being F:\ on Windows, it would be /media/<username>/my_thumbdrive, assuming that is the device name on linux. On Ubuntu, drives are usually mounted in the /media folder under your username. All your shared folders in Virtualbox will show up there, but not under your username.

/home Where your user files are stored (equivalent of C:\Users)
/media Where drives are mounted (In Ubuntu)
/bin Where system executables are stored (almost the equivalent of system32)
/lib Where the system stores the library files (like the .dll’s in system32)
/usr/bin Where extra stuff you install is stored, like python (almost equivalent of C:\Program Files)

/etc Where configuration files for various programs and network services are stored

(Equivalent to where C:\Program Files\ApplicationName files are stored)

/dev Where all the systems devices can be found. Since everything is a file in Linux, every hardware device also has a corresponding file under /dev

/tmp Where temporary files are stored (This is wiped upon reboot, unless configured otherwise)

/var Variable files—files whose content is expected to continually change during normal operation of the system—such as logs, spool files, and temporary email files.
/proc Where you can query the hardware for information e.g. cat /proc/cpuinfo
Your home folder location can be referred to as ~. So instead of typing out /home/me, you can just type ~ , and it’ll resolve to be the same path.

And that’s about the extent you need to know, and probably more so to be honest. /home/<username>/bin is a good place to store any shell scripts or whatnot that you want to run from any folder. Which brings us to our next topic…
Running your own scripts

Earlier in the table of commands, I mentioned the chmod command. Files created by you will almost always be only read write permission level, which is great from a security standpoint. However, say you want to run a python script. You could do python but that’s cumbersome. Instead, let’s do it the Linux Way™.

Header comment

The official name is the “shebang”, but in this guide I’ll call it the header comment – it’s a special type of comment you put at the top of a script in a Linux environment to tell the shell what  program to execute your program with. For a python script, you do this:

#!/usr/bin/env python

If we were writing a perl script, we would do

#!/usr/bin/env perl

If you were to write a bash script we would do:

#!/usr/bin/env bash

What it’s telling the shell to do is to look in the environment settings of the linux install, figure out where python is installed, and then run the rest of the source code through the python executable. This method has the benefit of not only being extremely portable (python might not be installed in the same place on all linux systems), it’s also super easy to remember what to write each time if you deal with multiple programming languages.

Linux doesn’t care about file extensions

With the header comment written, we now don’t have to worry about putting .py at the end of the filename anymore. You could name it “mypythonscript.jpg” if you wanted to – the data inside it is the same, and Linux just looks for that header comment, so it really doesn’t matter. It’s super nice to have no extension though, especially if you run the script a lot. You’ll just have to have your python scripts organized in a separate folder if you’re going to start foregoing extensions – hard to tell file types apart with no extension. The ‘file’ command can be used to identify which type of file a file is if you prefer to have no extensions.

Running your script

The first thing you have to do is mark it as executable. To do so, we’re going to use our trusty chmod command. We want to mark it as executable, so we’re going to use the u+x argument to add executable permissions to the file – This tells Linux to change the file mode to executible by the user only.

chmod u+x

Now, our script is executable. You can verify this by running ls, and it will now be green. Green means an executable file. To run it, we’re going to do


This is a security measure put in place by Linux so that you can be sure you are executing the file within the current directory – imagine if someone placed a malicious executable named ls in a folder, and you ran ls, and instead of executing the one in /bin, it ran the malicious one in your current folder? It wouldn’t be good.

In Linux, a single period is your current directory, and two periods is the parent directory. So


is really


If you have a script you do want to run from anywhere, put it in your bin folder in your home folder (~/bin). If you want to make that script or executable available for all users on the system, place it in /usr/local/bin.

Cancelling a process in terminal

To stop a process, hit CTRL+D. This will exit out of the current program (if you’re in an interactive python process, or if there’s a program you want to force quit in general, just hit CTRL+D) If that doesn’t work, use CTRL+C, but that isn’t a nice way of stopping a program, and its not recommended. Use as a last resort.

Previously, it was mentioned you can run multiple commands by either separating them with “;” or “&&”. The difference is that if you separate with a semicolon, you will have to force stop each command; For example if I run the following:

./; cp script_output backup/script_output; ./

If you force quit the instance of, it will continue on to copy the script_output file, which you’d have to force quit as well, as well as the A nice feature is that if has an error and fails, it will not continue on to run the copy command or the second python script.

Alternatively, if you use && to run multiple commands:

./ && cp script_output backup/script_output && ./

Now, when you cancel any one of these processes, the remaining processes will also be cancelled. However, if encounters an error, it will continue to run the second and third commands which may not be good – If cp ends up running the computer out of disk space and the second script generates more data, this could end badly. Choose the method of running multiple commands wisely. Personally I like using the && method better simply because I can force quit all of it.

To paste into the terminal, you must use CTRL+SHIFT+V. CTRL+V will not work to paste. Similarly, copying in the terminal must be CTRL+SHIFT+C.

Be careful when pasting commands into the terminal! If there’s a new line at the end of the command, it’ll automatically run the command!! (like if you hit enter after typing a command).

Multiline commands can be separated with \<enter>


cd \


Is the same As “cd /var/log” only in two lines, useful for long commands.

Package manager

No linux tutorial would be complete without an introduction to the package manager. This is a unique feature of linux – it allows you to install, update, and remove any piece of software on your computer. The syntax is very simple too. All package management must be run as root, or with “sudo” before it.

Apt – Advanced Package Tool

CommandWhat it doesExample
sudo apt updateUpdates the list of available software to install (if a security update for python got released yesterday, running update will let your computer know that)
sudo apt upgradeUpdates the installed software on your computer (applying that python security patch that it found out about through update)
sudo apt installAllows you to install a packagesudo apt install python3
sudo apt removeAllows you to remove a packagesudo apt remove vim
aptitudeLaunches the synaptics package manager – good for searching for packages. Can be run without root, but you can’t install anything without running as root.
Q to quit.
sudo aptitude

Older tutorials will use apt-get, which has since been superseded by Apt. Apt-get will still work fine, but apt is the new standard, and it has some nice improvements.

To easily search for packages in the repository, you can use Synaptic Package Manager, or you can

just google “how to install x on ubuntu” and you’ll find the package name. You can try guessing a package name, but you might not always be successful.

Pip is also directly accessible through the command line for python. Just run

sudo -H pip install

Python virtual environment

On your own machine, you have full root access, but on a work machine you most definitely will not. Having a python virtual environment allows you to install as many python packages with pip as you want, without needing to run sudo pip install <package>.

A good rule of thumb is to create a virtual environment for every project, separately, to separate dependencies from one environment to another.

An easy way to create virtual environments is to globally install a pip package called virtualenvwrapper.

To set up a virtual environment of python, create a directory in your home folder that you want the virtual environment to live in. Then run the following commands to create the virtual environment.

sudo pip install virtualenv

virtualenv pythonv

To make the python virtual environment your default python environment in your session, simply run

source /path/to/pythonv/bin/activate

Now when you run which python it will output /path/to/pythonv/bin/python.

Note that this is a temporary change – Closing the terminal or logging out will revert this change. Adding this to your ~/.bashrc file will execute it upon login, or you can set it as an alias in your bashrc.

Shell piping and redirecting IO

There are three types of pipe characters: <, >, and |. < is difficult to explain, so I left it out.

Pipe/Redirect characterWhat it doesExamples
>Redirects output to a fileman -k search > man_output.txt
>>Redirects output to file and appendsman -k find >> man_output.txt
|Takes the output of process A and puts it as input into process Bcat man_output.txt | grep “fast”
&>Redirect both standard output and error to same file.txt &> output.txt

In Linux, you have two main pipes – Standard Output (stdout, all your normal output of things that are printed to the screen), and Standard Error (stderr, when something doesn’t work right – Error on line 2, ‘;’ expected)

stdout is numbered pipe 1, and stderr is numbered pipe 2. By default, > is actually 1> – It’s redirecting standard output. If we wanted to redirect standard error, we would do 2>. 2>> will append, just like >> does. If we want to redirect both error and output, we can do &>.
This post and ubuntu / Linux / bash intro tutorial is based on work by mcvittal of reddit who licensed it under the WTFPL – Do What The Fcuck You Want To Public License. This post is here for archival and informational purposes.

Linux shell

Why you should switch to ZShell ( zsh )

Why use ZShell

It has some amazing features, but right out of the gate in no particular order:

  • Context based tab completion that puts most others out there to shame.
  • Shared history among tabs.
  • Dynamic Load modules
  • Spelling correction that out performs most others out there.
  • Globbing that works on magic. I am positive of this.
  • Themes that work wonders, there are tons of them out there and they fit everyone’s needs or just write your own!
  • Global aliases

I’m going to be an elitist and say bash is for the cavemen 😐 any machine you have a personal user account on: install zsh. life just became pretty… and pretty awesome. why zsh? well its powerful and configurable…. its awesome! and you can change a LOT about it and extend it via plugins.

sudo apt-get install zsh curl git-core ruby
wget --no-check-certificate -O - | sh

this should switch you to zsh and install an awesome script for zsh. if not then do the next two steps. They can be repeated at will. Note where your zsh is, most likely /bin/zsh.

which zsh

After that comes customization time! yay… etc.
(pick a theme, I prefer dallas so)
edit ~/.zshrc


Heres my plugins, you can remove the ones you dont need

plugins=(git ant cpanm debian github mercurial node npm svn)

Install rvm :

user$ bash -s stable < <(curl -s )

add the following to your ~/.zshrc

[[ -s $HOME/.rvm/scripts/rvm ]] && source $HOME/.rvm/scripts/rvm

more to come later.


Linux shell

Alsa CLI Volume control

I couldn’t find the silly volume control in the system settings one day so i figured there had to be something I could use to control volume settings like mic boost without needing a gui or remembering names and numbers for the CLI. well there is and it’s so easy a caveman could do it (hah remember those ads….)…. so without further ado here’s a fun and great way to control your volume via Alsa CLI Volume control.

type the following then use your arrows to move right/left and make the volume higher or lower by using up/down keys:

alsamixer -c 0

the 0 at the end is the number of your device. if a system only has one device you will use 0. if you have two devices you can use 0 or 1. it tells you the name of the device currently being edited so you don’t give yourself a heart attack by changing the wrong volume. picture of the control is attached.

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Android shell

Cyanogenmod Gapps error with SetupWizard

I saw that CM13 is out and it brings Android 6.0.1 (r17) goodies such as the battery saving ‘doze’ functionality and new permissions model, alongside the usual set of CM features. I have an HTC m8 sitting around which I figure was due for a custom rom right about now, so I downloaded and install a copy of CM 13 from everything went well as expected. I downloaded a copy of google apps from opengapps and installed it next and thats where things took a turn for the worse, as soon as I booted into CM i started getting errors of setup wizard being force closed over and over. I couldnt do anything but click the OK button over and over. So if you are getting a Cyanogenmod Gapps error this just may help you.

I booted into TWRP and tried fixing permission with no luck on next boot into system. I tried re-flashing everything from a clean install again with same results. I saw that you could report the issue so I clicked the submit button and it let me see the actual error that was being thrown which looked partially like :

AndroidRuntime: java.lang.RuntimeException: Unable to create application java.lang.SecurityException: addOnSubscriptionsChangedListener: Neither user 10069 nor current process has android.permission.READ_PHONE_STATE.

luckily I had enabled debugging before I installed gapps. so I connected my phone to my computer, booted up ADB, check out my post on some basic ADB commands here if you need a refresher, and granted the permissions needed for the issue to be resolved!

I checked for connected device :

adb devices

which gave me :

List of devices attached
FA43XXXXXXXX    device
emulator-5554   device

I then ran commands on my phone by connected to the shell on it and running my grant command:

adb -s FA43XXXXXXXX shell
pm grant android.permission.READ_PHONE_STATE

it gave no output and looked like this :

C:\Users\sumguy\adb>adb -s FA43XXXXXXXX shell
[email protected]:/ $ pm grant android.permission.READ_PHONE_STATE
[email protected]:/ $

This can be adapted for other such error also:

pm grant android.permission.ACCESS_COARSE_LOCATION

this seems to have resolved the issue for me and I was able to login to my account normally now with no crashes so far.

Linux shell

Linux distribution info & kernel info

Do you have multiple vms and real machines you use for random testing, and small tasks? need to know what machine you are on? what kernel you are using? what the current Linux distribution info is? what OS version did you last install on here? and more such questions? well! we have some of the answers for you. well maybe not answers, but more like small tools so you can get the answers!

Distribution info

lsb_release -a
on my ubuntu system it gives the following result :

$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu Xenial Xerus (development branch)
Release: 16.04
Codename: xenial

On a debian system it gives the following result :

# lsb_release -a
No LSB modules are available.
Distributor ID: Debian
Description: Debian GNU/Linux 8.4 (jessie)
Release: 8.4
Codename: jessie

If lsb_release -a doesn’t cut it for you then you can try
cat /etc/issue

as a result we see the following examples :

# cat /etc/issue
Debian GNU/Linux 8 \n \l

$ cat /etc/issue
Ubuntu Xenial Xerus (development branch) \n \l

In some cases where you suspect you are on centos or redhat, maybe because you noticed the package versions are old enough to be used by columbus while sailing the open seas, then you can use either

cat /etc/centos-release


cat /etc/redhat-release

which will give you result such as :

CentOS release 6.2 (Final)

Kernel Info

now as far as finding the kernel info goes you can get all the info you need via uname.

$ uname -a
Linux testhost 4.4.0-9-generic #24-Ubuntu SMP Mon Feb 29 19:33:19 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux
$ uname -r

as you can see uname -r gives you just the kernel version and uname -a gives you multiple pieces of info, like date the kernel was compiled, the arch (i.e. x86_64).