You can add or remove passphrase for your SSH private keys after creating your key pairs without creating a new key pair by using any of the following methods;

1. Interactive ssh-keygen

   $ ssh-keygen -p
   Enter file in which the key is (/home/user/.ssh/id_rsa):
   Enter new passphrase (empty for no passphrase):
   Enter same passphrase again:
   Your identification has been saved with the new passphrase.

2. Inline ssh-keygen

   $ ssh-keygen -p -P old_passphrase -N new_passphrase -f /home/user/.ssh/id_rsa
   Your identification has been saved with the new passphrase.

3. openssl

   $ openssl rsa -in ~/.ssh/id_rsa -out ~/.ssh/id_rsa_new
   Enter pass phrase for /home/user/.ssh/id_rsa:
   writing RSA key

You can easily view cellular network data usage in iPhone and iPad (any iOS devices in general). Available data includes total usage and breakdown of your data usage per apps. You can also reset the usage counter if you want to. That’s possible with these simple steps;

1. Launch the Settings app by tapping on the Settings icon on the Home screen or by searching for the app in the Spotlight Search.
   
2. Open Mobile Data.
   
3. View general data usage and breakdowns for each applications.
   
4. Scroll all the way down and tap on Reset Statistics.
   
5. Tap on the Reset Statistics option to confirm your action
   
6. Confirm that cellular data usage statistics has been reset.
   

SSH comes with 2 applications for remote file transfer, namely scp and sftp. You can also use SSH to secure your rsync session.

The easiest of these are scp. The command is quite similar to cp in copying local files except that you’ll have to specify the remote user and host in your command. For example,

scp myfile.txt [email protected]:/remote/folder/

will copy myfile.txt from your local folder to /remote/folder in 192.168.1.10. remoteuser need to exist and have write permission to /remote/folder/ in the remote system.

sftp in the other hand works almost exactly like ftp but with secure connection. Most of the commands are similar and can be used interchangeably. The following sftp example will work exactly as ftp would.

$ sftp [email protected]
Connected to 192.168.1.10.
sftp> dir
file1      file2  file3   
sftp> pwd
Remote working directory: /home/user
sftp> get file2
Fetching /home/user/file2 to file2
/home/user/file2                                                   100% 3740KB 747.9KB/s   00:05    
sftp> bye
$ 

You can also use ssh to secure your rsync session. To do this, use –rsh=ssh or -e “ssh” with your normal rsync commands. The following 2 commands will work exactly the same;

rsync -av --delete --rsh=ssh /path/to/source [email protected]:/remote/folder/
rsync -av --delete -e "ssh" /path/to/source [email protected]:/remote/folder/

Mplayer is initially a movie player for Linux, but through the many available options, it is capable of doing many other things, including to save, record or dump online music stream to file.

In it’s easiest form, running the following command will dump 1.FM’s Channel X (with more channels available from www.shoutcast.com) to current.mp3

$ mplayer -dumpstream http://64.62.252.130:8070  -dumpfile current.mp3

The following bash script takes this a little bit further by keeping the latest 3 dumps, and delete the older ones.

#!/bin/bash
URL=http://64.62.252.130:8070
WORKDIR=/home/shakir/temp/mplayerdump
MAXDUMP=3
CURRENTDUMP=`ls $WORKDIR | wc -l`
 
mv $WORKDIR/current.mp3 $WORKDIR/`date +%F`.mp3
if [ $CURRENTDUMP -ge $MAXDUMP ] ; then
   for i in `ls $WORKDIR | head -n $[($CURRENTDUMP-$MAXDUMP)+1]`; do
      rm $WORKDIR/$i
   done
fi 
 
mplayer -dumpstream  $URL -dumpfile $WORKDIR/current.mp3

Going a little further is to run the script through cron nightly, for daytime listening probably while being mobile and offline. Crontab entry is editable by the following command;

$ crontab -e

and add the following line (assuming the script is located at /home/shakir/mplayerdump.sh)

0 2 * * * /home/shakir/mplayerdump.sh

Do make sure the script is executable by running the following command:

$ chmod a+x /home/shakir/mplayerdump.sh

rar is a proprietary file format for file archival and developed by WinRAR. It provides Winrar to extract rar files in Windows and unrar for Linux.

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Safari‘s settings are available via the Settings app. Follow these steps to clear Safari‘s browsing history;

1. Launch the Settings app by tapping on the following icon on the home screen.
   
2. Scroll down and tap on Safari from the list.
   
3. Find and tap on Clear History and Website Data towards the end of the screen.
   
4. Tap on the Clear History and Data to confirm.
   

iOS 11 has native support for screen recording where you no longer have to jailbreak or connect your iOS devices’ to a computer to record.

1. Open Settings by tapping on the following icon on the Home Screen
   
2. Scroll down and tap Control Centre
   
3. Tap on Customise Controls
   
4. Tap on the + icon before the Screen Recording text
5. Screen Recording is now added to the Control Centre item
6. Open Control Centre by swiping up from the bottom of the screen
7. Click on the Screen Recording icon at the bottom of the Control Centre
8. The top bar turns blue to indicate that the screen is being recoreded
9. Tap on the blue bar to stop recording.
10. Tap on Stop to confirm your action
11. Open Photos
12. Go to Videos

Apache normally runs as an unprivileged user without shell access in most platforms. This is for security reason as a poorly written script or configuration if exploited will not escalate and cause much harm to the system.

If you’re running a development environment and know exactly what you’re doing, you can change the user and group that the Apache process runs as with these simple steps;

1. Find User and Group directives in Apache‘s configuration file.

   Apache configuration files

2. Set the user and group that you want Apache process to run as. The following example is to run it as root.

   User root
   Group root

   This could be a big security risk, especially to run it as root.

   Make sure the user and group has appropriate permission to DocumentRoot and related files and folders.

3. Restart Apache.

   How to restart Apache service

4. Check if the changes was successful

   $ ps aux | grep apache2
   root      1188  0.0  0.1 162184  6664 ?        Ss   Mar29   0:02 /usr/sbin/apache2 -k start
   root  1197  0.0  0.1 162184  5668 ?        S    Mar29   0:00 /usr/sbin/apache2 -k start
   root  1198  0.0  0.1 162184  5916 ?        S    Mar29   0:00 /usr/sbin/apache2 -k start
   root  1200  0.0  0.1 162184  5684 ?        S    Mar29   0:00 /usr/sbin/apache2 -k start
   root  1201  0.0  0.1 162184  5684 ?        S    Mar29   0:00 /usr/sbin/apache2 -k start
   root  1202  0.0  0.1 162184  5684 ?        S    Mar29   0:00 /usr/sbin/apache2 -k start

   In some distributions the Apache binary could be named httpd instead of apache2.

VirtualBox stores all the virtual machine files in a folder named VirtualBox VMs. The folder, by default, is within the user's home directory. It contains all the virtual machine's …
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Beginning version 7 of vim, it has this nice auto-completion feature. It is by default however limited to words that has already been in the current workspace. To use …
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