Wednesday, 22 September 2010

Basic Unix/Linux commands

In any type of testing (let it be functional or non-functional) some basic Linux/Unix skills could be very beneficial (if test environment is using that Operating System). Testers could connect to the server and perform basic tasks on their own releasing development team from some duties such as:
  • restarting the application server and/or the Operating System
  • accessing server logs to verify that the scripts are not causing server side exceptions not displayed in the browser
  • parsing server logs to calculate application load profile (i.e. number of concurrent users, pauses between requests, etc.)
The most common way to connect to the Unix system is to use SSH client such as Putty. This utility connects to the remote Unix server and allows for unlimited access to the server, provided that the user has sufficient access rights.
Open Putty session

It is considered a bad practise to share Administrator’s (or how it is called in Unix environment root’s) password with everyone and thus you should always use username with limited privileges for the day-to-day tasks.

The basic commands anyone connecting to the Unix server should know could be categorised into few groups.
  • Directory navigation and discovery
    • cd - change current folder to another (e.g. “cd /etc/init.d”)
    • ls - list content of the current folder often used with -lah attribute for additional info about file size, last modification data and permission (e.g. “ls -lah”)
    • pwd - displays current folder (e.g. "pwd")
    • find - search for files is a specified folder (e.g. “find /var/log -name .log”)
    • du - checks file or folder size (e.g. “du -hs /var/log”)
  • Text file processing
    • vi - very popular text editor for Unix operating systems; might be a bit difficult for a non-experienced user. Easier alternatives would be “nano” and “pico”
    • cat - prints file content in the console (e.g. “cat /var/log/messages”)
    • less - text viewer which allows backward navigation (e.g. “less /etc/passwd”); to quit press Ctrl+C
    • echo - prints text passed to the command in the console or sends it to the file (e.g. “echo “Hello World” > /tmp/filename.txt”). Can also be used to clear content of the file (e.g. “echo -n /tmp/zimbra.log”)
    • grep - filters the file or result of other command and prints lines containing search term (e.g. “cat /tmp/server.log |grep error” or “ps aux |grep apache”)
    • sed - command line version of the search and replace utility (e.g. “cat file.txt| sed -e "s/SearchFor/ReplaceWith/g" > ResultFile.txt”)
    • awk - pattern scanning and text processing language. Following example will parse /etc/passwd file using colon as a field delimiter (-F:) and print the content of the second column for each record (e.g. “cat /etc/passwd| awk -F: '{ print $1 }'”)
  • Operating System - Process control
    • ps - list all processes running in the system (e.g. for linux “ps aux” and for unix “ps -ef”)
    • kill - forces the process to quit (e.g. “kill -9 ProcessID”); Process id can be found by executing ps command
    • killall - terminates all processes by the process name (e.g. “killall zimbra”)
    • free - displayes amount of free and used memory in the system (e.g. “free”)
    • top - lists all processes and sort them by CPU usage (e.g. “top”); to quit press Ctrl+C

If the only reason for accessing Unix server is to read/modify files or transfer files between the server and the local workstation it might be a better option to use other tool with graphical user interface (to which Windows users will be more used to) such as WinScp.

WinScp uses SSH protocol (which is the same protocol Putty is using) to connect to the Unix server and transfer files over secure connection to and from the local host.

The tool provides two different connection options (i.e. scp, ftp). FTP will only work if the FTP server is running on the remote server wheres scp will work always as it is using SSH connection for file transfers. Both options are equally secure as all the data is sent over secure SSH channel.

Both tools are free to use and their small size (around few MB) makes them ideal to use out of the memory stick.


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