In this post I will be making a list of great Linux cmd’s that I find all over the net one great place to stop by is commandlinefu.com they have a great deal of important linux cmd’s.

First cmd is mtr, it combines your ping and netstat cmd’s. In CentOS you have to su- to run this cmd:

mtr google.com

The following cmd I just started using recently and it has been a life saver I don’t know how I went all that time without it. The cmd is screen it works like your VNC or NX but for the terminal, it is especially handy if you SSH into your box but you don’t want to leave the terminal running waiting for a task to finish, you just start a screen run your cmd and detach from the screen. Now even if your connection gets disconnected or you disconnect yourself all you have to do when you connect again is run “screen -dR” and you are connected back to your earlier session and you can check on the progress of your task. To list screen instances “screen -ls”.

screen

Ctrl+a   ->pressing this twice moves to the next screen

Ctrl+a+c  ->adds a new screen to you screen instance

Ctrl+a+d ->detach from screen session

Ctrl+d  ->exit a screen

screen -dR   ->connect to/start a screen session

Mount a drive world writeable

mount -t ntfs-3g -o umask=000 /dev/drive /mnt/mountpoint

mount -t cifs -o umask=000,username=username,password=password //ipaddress/folder /mnt/mountpoint

by adding the option umask=000 any user can write to the mounted folder, this comes in handy when you want to write to a mounted drive as a regular user.  I have had a problem with some slack based distro’s not accepting this option in the current format and might need to play around with the mask cmd placement to see what works.

I just upgraded to CentOS 5.5 and while talking to a friend of mine we got into talking about updating vs clean install. After my update I had to restore to an image before the update as my mail system was not working, checked all packages contained in the update and zeroed the cause to a sendmail update. Which was disabling my current MTA “postfix”. I fixed that and another issue with my open office and I was ready to go. While my friend prefers to just do a clean install.

To me it just comes down to preference, if you have a heavily customized system it’s time saving to just do an upgrade, but if you are running a generic system with few modifications a clean install might be the best way for you.

The one good thing about Linux is the range of distributions available. Every few months I will load a new Distribution on my flash drive or make a Live cd and try it out. I am currently trying out Linux Mint and I like it, I would definitely recommend it for new users it comes loaded with most apps that you need day to day. It’s eye candy is one of the best I have checked out so far, I even loaded it onto one of my old boxes that am planning on donating.

If you help fix people’s computers you will come across devices that windows will not have drivers for or you may be having problems downloading them from the machine manufacturer site, here is a quick way to go about it.

Go to Device Manager right click on unrecognised device there will be an exclamation mark on it click Properties ->Details and select Hardwae ID’s from the property drop down list. VID_ and VEN_ are used to identify vendors and PID_ and DEV_ identify Product ID. The HEX value following Product ID “PID_/DEV_” or Vendor ID “VID_/VEN_” is what you use in your search to identify the device.

Now go to pcidatabase.com enter your product or vendor id to such for your device.

I was trying to work on a computer the other day, it would not recognize it’s DVD drive and switching with another dvd drive did not make a difference. The error message provided was
“Windows cannot load the device driver for this hardware. The driver may be corrupted or missing. (Code 39)”

To solve this Code 39 error, follow these instructions:

1) Close all open programs

2) Click on Start, Run, and type REGEDIT and press Enter

3) Click on the plus signs (+) next to the following folders

• HKEY_LOCAL_MACHINE
• SYSTEM
• CurrentControlSet
• Control
• Class
• {4D36E965-E325-11CE-BFC1-08002BE10318}

4) This folder is the DVD/CD-ROM Drive Class Description in the registry. Look for any of the following names in the right hand column.

• UpperFilters
• LowerFilters
• UpperFilters.bak
• LowerFilters.bak

5) If  any of the above keys shown in step 4 are listed, right-click on them and choose Delete
6) After deleting the keys, close the Registry Editor
7) Reboot your computer
Open My Computer and check to see if your CD or DVD drives have returned. You may also want to open Device Manager and verify that the yellow exclamation and error code on the CD or DVD drive is gone.

I got this info at this site and they even tell you other things you can do with drive errors.

Like most people I prefer to use centos supplied apps from their repos as it just makes keeping things updated easier. So I use the eclipse supplied by centos which does not have Junit4 if you would like to enable it here are the steps I followed:

1.Download eclipse from there site the .tar version

2.Extract folder org.junit4_4.5.0.v20090423 and file org.eclipse.jdt.junit4.runtime_1.1.0.v20090513-2000.jar and copy them to folder /usr/share/eclipse/plugins/ download file junit-4.1jar and place it in folder org.junit4_4.5.0.v20090423

3.Restart eclipse and you should be set. Happy Testing!!!!

NB: Depending on the eclipse version you download the numbers on the folders and files may be different, and incase the new versions require a different file than junit-4.1.jar eclispe will tell you the new version needed.

the Junit-4.1.jar I used is here or you can google it if you want.

I have read hundreds of articles with the above headline but it wasn’t until I read this article that I realized just how far Linux has come, the fact that it can compete toe to toe with an advanced os like OS x is just insane let alone come out ahead. I can’t wait to see in the years ahead how Linux evolves, I have been using it for the last 5 years and am still impressed and always learning new things about it.

I found this neat cmd to use when trying to find files larger than certain sizes e.g

find / -type f -size +200M

If you want files less than that size you can do

find / -type f -size -200M

For other ways to use the cmd check out this post where i got the info from.

This other cmd finds files larger than 10M and calculates their sizes too.

find / -size +10240000c -exec du -h {} \;

Remember in all cases to change “/” to the location you want to search for the files e.g “/home/username”.

By default Gtkpod uses xmms to try and play songs from your Ipod, a few linux distributions come with xmms. If yours came installed with it first remove it as it does not play music from your Ipod. Then go ahead and install
xmms-mp3

You should now be able to play music from your Ipod with Gtkpod. Although xmms is not the latest player I like it because it’s small and lightweight.

For a single file:

ffmpeg -i -acodec libmp3lame -ar 22050

For a bunch of M4B files:

for m4b in $(ls -1 *.m4b); do ffmpeg -i $m4b -acodec libmp3lame -ar 22050 ${m4b}.mp3; done