Monthly Archives: September 2015

The script /etc/rc.local is to be used by the systems administrator. It is executed after all the normal system services has been started. Administrators can use it to get the summary of the server(like memory status, hardware status, and others). The reports can be sent to personal mail ID. The following is an entry inside the /etc/rc.local file:

# vi /etc/rc.local
‘echo last’ | /bin/mailx –s “Last Logged-in users in system “ user@gmail.com

Save the file by presenting :wq!

Next time, when the server boots, a mail will be thrown with the report of the last logged-in user’s information- the same way programs or scripts can be placed inside /etc/rc.local, as shown below.

Here’s a program example:

/opt/Tivoli/tsm/client/ba/bin/dsmc sched > /dev/null 2>&1 &

This is used to start the TSM( Tivoli storage manager) client to run a backup.

It is a very common requirement to remove duplicate file. If you have a large collection of file, then finding and removing such duplicate file will be a tedious task. But this is where GNU/Linux makes the difference- it provides the ‘fdupes’ utility, which finds duplicate files by comparing their check- sum.

Let us install the ‘fdupes’ command using an aptitude package manager.

$ sudo apt-get install fdupes

Now, let’s suppose that we have a large collection of files and we want to remove all duplicate files. We can use the ‘fdupes’ command with the ‘-d’ option, which displays the list of duplicate files and prompts users to select which files they want to preserve. Let us check it out with an example.

First create a few duplicate files

$ for I in {1.10}; do echo “ Opensource for You.” >
F${i}.txt; done

Now find and remove them.

$ fdupes –d .

[1] ./f2.txt
[2] ./f3.txt
[3] ./f5.txt
[4] ./f9.txt
[5] ./f6.txt
[6] ./f8.txt
[7] ./f4.txt
[8] ./f1.txt
[9] ./f10.txt
[10] ./f7.txt
Set 1 of 1, preserve files [1-10,all]: 1 # Preserve only one copy of file
[+] ./f2.txt
[-] ./f3.txt
[-] ./f5.txt
[-] ./f9.txt
[-] ./f6.txt
[-] ./f8.txt
[-] ./f4.txt
[-] ./f1.txt
[-] ./f10.txt
[-] ./f7.txt

In the output , the ‘+’ sign before the file name means the file has been preserved and the ‘-‘ sign means the file has been deleted.

Working on the Linux command line means switching between a lot of directories. Suppose you are in Directory ‘A’ and then move to Directory ‘B’. When you want to come back to Directory ‘A’, typing the complete directory path for ‘A’ can be cumbersome sometimes. Here’s a simple trick for this. You can use ‘cd-‘ to go back to the last directory you were in.




Lets see how this works by using an example:

Your current working directory is:

$ pwd
/home/himanshu

Your new working directory is:

$ cd /usr/local/bin/

The following command takes you back to your old working directory:

$ cd –
/home/himanshu

So you can see that it’s easy to switch between two directories using ‘cd-‘.

But, ‘cd –‘ resolves only part of the problem. It can only switch you back to the last working directory. What if you switch between multiple directories and then want to return to the first or some other desired directory? I mean, suppose you begin in Directory ‘A’, then want to return to Directory ‘A’.

For this, you can use the combination of ‘pushd’ and ‘popd’.

Here is an example:

$pwd
/home/himanshu
$ pushd /home/himanshu
$ cd /usr
$ cd /tmp
$ cd/proc
$ popd

—
$ pwd
/home/himanshu

As you can see, you first pass the desired directory(to which you want to come back to eventually) as the argument to ‘pushd’. Then through ‘popd’ you can actually trigger a directory switch to that directory from anywhere on the command prompt.

Although running the scp or ssh command is very command is very convenient, mounting the remote servers filesystem on the local system has solved many problems for me.

Here is how this can be done. To mount the remote filesystem to a local Linux workstation, you need to install the sshfs. To install, you can choose to use the package manager of your distro or you can compile and install manually.

After the installation is complete, you can run the following command on your Linux workstation:

sshfs username@hostname://