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  • in Linux
  • 2 min read

SimpleHTTPServer with SSL

python -m SimpleHTTPServer

and the result:

jorge@applepie:~ $ python -m SimpleHTTPServer 8080
Serving HTTP on 0.0.0.0 port 8080 ...

It listens on all IPv4 interfaces, and binds to the port you specify, which in my case is 8080. The person on the other side will then be able to access the files in the directory from the outside by going to http://server1.example.com:8080, provided that your machine has the hostname server1.example.com, and that you have the port 8080 forwarded to the IP of server1.

  • in Windows
  • 1 min read

sysprep – a fatal error occurred

I’m currently testing out Windows Deployment Services, and while working with sysprep on a Windows 7 Pro client machine, I got the following error:

sysprep error

Nothing seemed to work, till I tried the following recipe:

Open the run-menu, type in regedit and go to HKEY_LOCAL_MACHINE\SYSTEM\Setup\Status\SysprepStatus. Find GeneralizationState and set the value to 7.

Run a command prompt with administrative privileges. Type:

msdtc -uninstall
msdtc -install

Open up regedit again and find HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\SoftwareProtectionPlatform. Find SkipRearm and set the value to 1.

net stop WMPNetworkSvc

Try running sysprep again now. Hopefully it should work. That’ll save you some time of frustration and hopefully you won’t go bald sooner.

Should this not work, check the sysprep-log file at C:\Windows\System32\Sysprep\Panther\setuperr.txt.

VMware, i3 and multiple monitors

For a while now I’ve been trying to set up VMware to work with multiple monitors, in a Linux guest. With some windowmanagers it works out of the box without any issue, such as with Unity. I never figured out how to do it with xmonad, and recently I switched to i3 just to try something new. The damn “Cycle multiple monitors” button didn’t work here either. When I tried it, a message popped up saying:

The virtual machine must have up-to-date VMware Tools installed and running.

  • in Linux
  • 4 min read

ncat, a modern implementation of netcat

ncat is a utility that is like the UNIX cat command but for network connections. It’s based on the original netcat and comes with a couple of more modern features.

In this short post, we’ll go through a couple of examples to see exactly what uses this tool has. I’m currently using ncat version 7.01, in Ubuntu 16.04. ncat is a part of the nmap package in Ubuntu.

  • in Linux
  • 1 min read

Split a file into a number of equal parts

As an example, we have a file named primary_data_file.txt that contains 616 lines of data. We want to split this into 4 files, with the equal amount of lines in each.

$ wc -l primary_data_file.txt 
616 primary_data_file.txt

The following command should do the trick:

split -da 1 -l $((`wc -l < primary_data_file.txt`/4)) primary_data_file.txt split_file --additional-suffix=".txt"

The option -da generates the suffixes of length 1, as well as using numeric suffixes instead of alphabetical.

The results after running the command are the following files:

$ wc -l split_file*
  154 split_file0.txt
  154 split_file1.txt
  154 split_file2.txt
  154 split_file3.txt
  616 total
  • in Linux
  • 1 min read

Test if a port on a remote system is reachable

With telnet:

telnet webserver.example.com 80

With bash:

cat < /dev/tcp/webserver.example.com/80

Replace tcp with udp, depending on what you want.

With netcat:

nc webserver.example.com 80 &> /dev/null; echo $?

If the port is open, you will get an output of 0. If it’s closed, it’s a 1.

  • in Snippets
  • 1 min read

Compare the output of two commands

..without creating a temporary file:

diff -y <(ls First_directory) <(ls Second_directory)

The -y is just to show a side-by-side comparison. Very handy! And the result?

[jorge@j-laptop temp]$ diff -y <(ls First_directory) <(ls Second_directory)
common.txt                          common.txt
first_file.txt                            | second_file.txt

Thanks to my colleague Ingvar for showing me this!

  • in Linux
  • 1 min read

No Wi-Fi device found

I just reinstalled one of my machines with Fedora 21. The install went great, but when the machine was done rebooting, and I was trying to set up my access to a wireless network with nmcli (NetworkManager), I got the following error-message:

# nmcli dev
DEVICE   TYPE      STATE        CONNECTION 
enp0s25  ethernet  unavailable  --         
lo       loopback  unmanaged    --         
wlo1     wifi      unmanaged    --

..and:

# nmcli dev wifi rescan
Error: No Wi-Fi device found.

Spending a lot of time finding what the problem was, I finally found the solution. It seems that Wi-Fi support in NetworkManager has been separated to a plugin. The package NetworkManager-wifi was missing. According to Pablo S. Torralba, who was kind enough to comment on this post, it should be enough to kill NetworkManager and launch it again as root. Should that fail, you can always try the old reboot-trick! Either way, it should hopefully be working.

  • in Linux
  • 3 min read

Introduction to cron

cron is a time-based job scheduler. This piece of software utility is used when you need to have a program run repeatedly at set time.

The daemon that runs in the background is named crond, while the file that contains the jobs themselves is named crontab.

You have three main directories:

  • /etc/crontab is the main system crontab file.
  • /var/spool/cron/ a directory for storing crontabs defined by users.
  • /etc/cron.d/ a directory for storing system crontabs.

Creating

Creating a crontab-file for your user is easy. Usage depends on what you need to do.

Edit

crontab -e

This command will allow you to edit the current user’s crontab. If a crontab doesn’t already exist, it will create a new one once you have saved your changes.

Edit another user’s crontab

crontab -u jorge -e

You can also edit another user’s crontab, but only if you have the correct permissions in place to do so.

List

crontab -l

or

crontab -u jorge -l

..to list another user’s crontab.

These are the most common usages of the command crontab. For a couple of more options, see man crontab.

Syntax

The syntax of a crontab-file looks like this:

* * * * * /path/to/program

Each asterisk represents a field. Starting from left to right, the fields are as follows:

  • Minute (0 – 59)
  • Hour (0 – 23)
  • Day of month (1 – 31)
  • Month (1 – 12)
  • Day of week (0 – 7, where 0 and 7 is Sunday)

On the fields Month and Day of the week, you can also use names instead of numeric values.

Operators

There are various operators that you can use with cron. Here’s the list:

Asterisk (*)

An asterisk (*) is used to indicate that every instance (i.e. every hour, every weekday, etc.) of the particular time period will be used. So if you use an asterisk in the field Hour, it means that it will run every hour.

Comma (,)

With this operator you can specify a list of values. If you use 1,5 in the field Day of week, this would mean Monday and Friday.

Dash (-)

While comma specifies a list of values, dash specifies a range. 1-5 in the field Day of week would mean Monday to Friday.

Forward slash (/)

Forward slash specifies a step value. If you’d like to execute a command every other hour, you could use 0-23/. You can also use steps after an asterisk, so if you want the command to run every two hours instead, use */2.

Examples

First

45 14 1 * * /home/jorge/backup.sh

In this example the script backup.sh runs at 14:45, the first day of the month, every month.

Second

30 04 1,15 * 5 /home/jorge/list_files.sh

This line runs the command list_files.sh at 04:30 on the 1st and 15th of each month, plus every Friday.

Third

00 08 * * 1-5 /home/jorge/wake_up.sh

The line above runs the command wake_up.sh at 08:00, Monday to Friday.

Fourth

*/5 * * * * * /home/jorge/annoy_wife.sh

..and this line would run the program annoy_wife.sh every five minutes, every day.

As always, if you want to know more about cron, check out the command man cron.

Have fun!