Question

I am writing a simple script which restarts a hadoop slave. In the script, I have to do some initial changes as a root user. After that I have to change to user “hadoop” and perform set of commands. I was using os.system to run commands but I doubt whether it works well. For example:

uid=pwd.getpwnam('hadoop')[2]
os.setuid(uid)
os.system('whoami')
os.chdir('/home/hadoop/hadoop/')
os.system('bin/hadoop-daemon.sh stop tasktracker')

Again I have to perform some commands as root after this and again become user “hadoop” and execute :

os.system('bin/hadoop-daemon.sh stop tasktracker')

I have three questions here ,

1. Is os.system is the best command that I can use to issue linux commands ?

2. I am able to change from root user to user hadoop by the commands above but I am not able to change to root user (I can understand there will be security issues if they permit this, I want to know is there any possibility to do that , atleast by passing password) ?

3. Does os.setuid() work ? whoami prints user hadoop but the process “tasktracker” is not stopped using those command, but if i perform the same commands manually it works fine (I use “su hadoop” instead of setuid while trying it out manually).

Thanks for all your help.

• Sethu

Answer 1

you could use:

os.system('sudo -u hadoop bin/hadoop-daemon.sh stop tasktracker')

or if you dont have sudo, but have su

os.system('su hadoop -c "bin/hadoop-daemon.sh stop tasktracker"')