Linux Tips

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Revision as of 14:15, 19 November 2011 by Roux (talk | contribs)

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Using ssh

  • you work on a computer and you want to easily connect another distant computer without entering you password at each time. To do so, you must generate a private and a public key on your computer to be put on the .ssh directory on your home, using, for instance, the dsa protocol:
ssh-keygen -t dsa

Then, you have the two new files in the ssh directory

id_dsa
id_dsa.pub

Add the public key id_dsa.pub to the list of keys in the .ssh/authorized_keys file of the distant computer (create the file if it does not exist). Now it should work for you!

In addition, you can simplify the connection by configuring your ssh. Edit the .ssh/config file on your computer and enter

StrictHostKeyChecking no

Host RemoteComputer
       Hostname computer.domain.com
       User username
       Protocol 2
       ForwardX11 yes

Protocol 2 is for ssh2 and ForwardX11 enables you to open a remote Xwindow. Typing

ssh RemoteComputer

or

scp RemoteComputer:File .

is now sufficient to connect the distant computer without entering your password. You can add several Host in this file.

  • you want to execute a single command on a distant computer without connecting to the computer.
  • ssh tunnels... (to be done)

Handling batch jobs

  • if you want to send a job on a computer and logout without killing the job:
:> nohup ./job

Transferring files

  • the scp command:
:> scp server:directory here
  • if you do some regular updates, there is no -update option to scp. Then, better use the rsync command. For instance with
:> rsync -avub -e ssh server:data/*.gz data/

be careful with the slash after directory names, with or without is no exactly the same behavior. Look at man rsync before using it.

Working with zip files

Linux usually provides a couple of command piping gzip

zgreg, zcat, zdiff, zless, zmore, zegrep,...

Here is a simple extension of tail and head for zipped files, that you can call ztail and zhead (example is for tail, replace "tail" with "head" everywhere to get zhead) and add to your own /bin directory:

#!/bin/bash
PATH=${GZIP_BINDIR-'/bin'}:$PATH

usage="Usage: $0 [OPTIONS]... [FILES]...
Like 'tail', but operate on the uncompressed contents of any compressed FILEs.

Options are the same as for 'tail'."

case $1 in
--help)    exec echo "$usage";;
-h)        exec echo "$usage";;
esac

options=""
files=""
for i in $@; do
str="$i"
if test -f $i && [ ${str:(-3)} = ".gz" ]; then
    files=$files"$i "
else
    if [ ${str:0:1} = "-" ] && [ $str != "-v" ] && [ $str != "--verbose" ]; then
        options=$options"$i "
    elif [ $str != "-v" ] && [ $str != "--verbose" ]; then
        echo -ne "***Warning: $i is neither a regular zip file or a regular option***\n\n"
    fi
fi
done

for file in $files; do
    echo "==>"$file"<=="
    exec gzip -cd $file | tail $options
done

The coma to point conversion in French environment

if you are working with a configuration of Linux which has not the dot "." as a standard format for floating points data (for instance the coma "," in French), you can add the following two lines in your .bashrc file:

LC_NUMERIC=en_US
export LC_NUMERIC

this will make the job without too many side effects.