If you need to test in a bash script if a file exist you can launch the following command.
Note if the file exist , but , is empty this also test true and tell you that the file exist
Author: Fabien
space char directly after var in bash
In bash space is used to determine the end of a variable ,
for example when you launch
this will display abcd ef ,if you try to to display abcdef you can‘t do echo $varef
the solution to this little problem is : is to use curly brackets.
will display abcdef
Installing Jellyfin on a Rasberry PI4 (Rasbian Buster)
The openSSL problem is now corrected , you should not be obliged to do what is described in this page
As soon as the raspberrypi foundation announcement of the new raspberry pi was made. I was sure it was going to be a great headless media server for my network.
with the Rasberry pi 3b and the severe lack of bandwidth on the ethernet and the USB2 ports , using the device as a media server wasn’t really practical.
Now that i received my Raspberry pi 4 B 2GB edition i looked at what was available in term of good media server and I heard about Jellyfin . a pretty features full media server .
I first installed the release of raspbian buster lite available on the raspberry pi website , then activated the ssh by creating an empty ssh file in the boot partition, ran sudo apt update && sudo apt upgrade and was soon ready for the next step
After i was ready to install Jellyfin , i went to the official jellyfin website and started reading the installation instructions.
Raspbian is a tuned version of debian so I chose the instructions regarding debian and launched the following commands :
After downloading more or less 400MB, the installation was completed ,
but the server wasn’t responding on the 8096 port !
after launching the command netstat -tlp on my raspberry I figured out the port wasn’t even opened.
Weirdly systemctl status jellyfin.service was telling me the service was active and running ,
shortly after that i located the log of the application ( /var/log/jellyfin/jellyfin )
/var/log/jellyfin/jellyfin
[2019-06-30 12:40:10.020 +01:00] [INF] Jellyfin version: "10.3.5.0"
[2019-06-30 12:40:10.113 +01:00] [INF] Arguments: ["/usr/lib/jellyfin/bin/jellyfin.dll", "--restartpath=/usr/lib/jellyfin/restart.sh", "--ffmpeg=/usr/lib/jellyfin-ffmpeg/ffmpeg", ""]
[2019-06-30 12:40:10.147 +01:00] [INF] Operating system: "Linux" "4.19.50.7"
[2019-06-30 12:40:10.148 +01:00] [INF] Architecture: Arm
[2019-06-30 12:40:10.156 +01:00] [INF] 64-Bit Process: False
[2019-06-30 12:40:10.156 +01:00] [INF] User Interactive: True
[2019-06-30 12:40:10.157 +01:00] [INF] Processor count: 4
[2019-06-30 12:40:10.158 +01:00] [INF] Program data path: "/var/lib/jellyfin"
[2019-06-30 12:40:10.159 +01:00] [INF] Web resources path: "/usr/lib/jellyfin/bin/jellyfin-web/src"
[2019-06-30 12:40:10.159 +01:00] [INF] Application directory: "/usr/lib/jellyfin/bin/"
this log wasn’t helping at all it was just the same 10 line repeating over and over again, i just knew something prevented the launch of the application ,it was a starting loop, but the log wasn’t verbose enough for useful information to be logged.
After unsuccessfully trying to remove and reinstall jellyfin i tried to run the application manually and not from her service.
i first stopped the service by launching
Then launched the app by
and BINGO , i got the message No usable version of the libssl was found
after a little googlefu I figured-out the libssl installed by default in raspbian buster was too new and was causing an issue with jellyfin
my version was ssl 1.1.1c and i needed a 1.0.x version
So , to force my system to use a old version of this library without having to recompile half the OS , i created the file : /etc/apt/sources.list.d/jessie.list
and written inside the following lines :
i then launched the commands
after theses last commands , your raspberrypi is now ready to launch Jellyfin.
you can do it with
you can now access the webserver of your media server on the tcp port 8096
bash : Random number in OpenWRT
On some light linux environement running busybox or openWRT you will notice that you don’t have access to the $RANDOM variable ,
the date command is also incomplete so you can’t use the tail of the nanosecond date to have a random number.
.
Using this command you will get a random number beetween 0 and 69.
if you wish to change the range of the random numbers , just edit the regex in the grep part
Using AWK to display the min the max and the average of a list
awk is a extremely powerful tool !
i’m always surprised how much you can do with it.
My latest finding is pretty amazing.
Lets say you have a list of numbers , and you want to figure out the bigger number , the lower number , and the average of all the numbers in the list.
you can use the following awk code to print minimum, maximum and average.
The output is going to be :
avg 32.93 | max 100.1 | min 1.5
you can also use this code with decimal numbers
Bash – Loop over the content of a file line by line
If you need to iterate over the content of a file line by line
You can use this little bash trick.
In this case , it will simply print the line, but if you need to do an operation on the text , just insert your code into the while loop.
How to update Grafana from version 4 to version 5
Grafana is a wonderful tool to display time series ans a lot of different metrics
The project is in a very active development state , and new features are added constantly.
The version 5 is particularly desirable since a new layout engine for the dashboard has been developed, and is quite powerfull !
So to update your install of Grafana from 4 to 5 you need to launch several command with root or a privileged user.
The service should automaticly restart when the update is done , but check that it is running with :
service grafana-server status
You should see something like this
? grafana-server.service – Grafana instance
Loaded: loaded (/usr/lib/systemd/system/grafana-server.service; disabled)
Active: active (running) since ven. 2018-04-20 17:47:41 CEST; 1 day 22h ago
Use the keyboard on a remote machine over SSH?
If you use a Linux box to display some infos in a public space , you might not have the possibility to connect a mouse and keyboard every time you need to click on the page.
For example, at work we use a TV to display some metrics with grafana,
Sometime, when we reboot the machine , the identification cookie will be outdated and the browser will land on the authentication page instead.
Since the machine has no keyboard and mousse attached this cause some issues , .
So I’ve used the tool xdotool that allow a privileged ssh user or a script to interact with the mouse and keyboard
An important step is to select the screen on witch you want to send mouses clicks and keystrokes.
After that lets say your screen is displaying a full-screen browser with a login page ,
By default the cursor is already in the login form.
for the example , the login/password are going to be admin/admin
you are now logged and you dashboard will display
Bash keyboard shortcuts
When you are spending your day in the terminal , you will find that navigating using only the arrows keys although fine at the the start will frustrate you because it’s quite slow.
Bash come with a lot of keyboard shortcuts design to gain precious time.
CTRL+A # will move the cursour to the beginning of the line
CTRL+E # moves to end of line
CTRL+C # halts the current command and back to prompt
CTRL+D # deletes one character backward or logs out of current session, similar to exit
CTRL+K # deletes all the text forward to the end of the line
CTRL+L # clears screen and redisplay the line
CTRL+R # searches history entering keyword ,
CTRL+T # transposes two characters
CTRL+U # kills backward from point to the beginning of line
CTRL+W # kills the word behind the cursor
i’ve put in bold the shortcuts that i use every day , i don’t use CTRL+A and CTRL+E because the keyboard has keys that are foing the same thing.
Bash brace expansion. (to delete files)
In bash , it is common to have to do some action on a numéric serie of files , like deleting or renaming ,
Using brace expansion you will be able to générate a single line that will act on multiple targets ,
For our example , let’s think about a list of ten files
in the simple case where i want to delete the complete list of files, i just have to run de command,
The 10 files will be deleted, but , this is not practical if you want to keep the last file , and delete the other nine,
In that case we can use a usefull tool called brace expansion,
To delete the files 1 to 9 , i just have to run in my bash terminal!
This last one is extremely practical , I use it very often in a lot of different uses cases.
But in other cases , you may want to delete even on odd files , or one every three files,
This is also doable with braces expansions