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I have implemented a small beowulf cluster for testing purpose, all nodes with Ubuntu server 18.04.

I have installed pdsh for running the same command on ssh at the same time on multiple node. ssh login is granted passwordless with public/private key distribution over the nodes (example: https://www.rittmanmead.com/blog/2014/12/linux-cluster-sysadmin-ssh-keys/) .

If I try a simple command like "date" , all is fine:

me@master:~$ pdsh -w me@node[0-3] date
node0: Mon Mar 9 18:56:04 UTC 2020
node2: Mon Mar 9 17:26:15 UTC 2020
node3: Mon Mar 9 16:42:37 UTC 2020
node1: Mon Mar 9 17:42:52 UTC 2020
me@master:~$

But if I try a command that require a sudoer privileges like this:

me@master:~$ pdsh -w me@node[0-3] apt update

then it returns these errors:

node0: WARNING: apt does not have a stable CLI interface. Use with caution in scripts.
node0:
node0: Reading package lists...
node0: E: Could not open lock file /var/lib/apt/lists/lock - open (13: Permission denied)
node0: E: Unable to lock directory /var/lib/apt/lists/
node0: W: Problem unlinking the file /var/cache/apt/pkgcache.bin - RemoveCaches (13: Permission denied)
node0: W: Problem unlinking the file /var/cache/apt/srcpkgcache.bin - RemoveCaches (13: Permission denied)
pdsh@node00: node0: ssh exited with exit code 100

and so on for all other nodes.

The problem is the "apt update" command that require a sudo execution but I have not found a way to pass it with pdsh

The same kind of commands launched with "real" root user runs fine:

root@master:~$ pdsh -w root@node[0-3] apt update

But in this case this means actually enabling the "real" root user on all nodes, which I would like to avoid.

Is it posssible? Is there a way for running elevated privileges commands with pdsh without enabling the root user? Or are there alternative tools that can do this?

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8
  • Is there a reason you can't run pdsh -w me@node[0-3] sudo apt update? Will it not ask for a password or something?
    – mchid
    Apr 3, 2020 at 17:00
  • 1
    If I run : me@node0:~$ pdsh -w me@node[0-3] sudo apt update This is the results: node0: sudo: no tty present and no askpass program specified pdsh@node0: node0: ssh exited with exit code 1 ... And so on for nodes 1, 2 and 3 :-\ B.
    – bed
    Apr 4, 2020 at 17:06
  • Thanks, it's just a guess but try this instead: pdsh -w me@node[0-3] sudo -S apt update If you still have trouble, try this: pdsh -w me@node[0-3] echo "password\n" | sudo -S apt update but replace password with your actual password and don't forget to put the new line character: \n after, as this is needed.
    – mchid
    Apr 4, 2020 at 17:36
  • Please let me know if this works and I will make it an answer. However, I will keep looking for a better solution in case you don't want your password in plaintext like this.
    – mchid
    Apr 4, 2020 at 17:38
  • Running pdsh -w me@node[0-3] sudo -S apt update the bash freezes waiting for something, then ctr-c : interrupt,.. command in progress node0... and nothing happens (other 2 ctrl-c for interrupt). For pdsh -w me@node[0-3] echo "password\n" | sudo -S apt update I think there is a typo, there must be a space, like this: pdsh -w me@node[0-3] echo "password" \n | sudo -S apt update; in any case the result is: [sudo] password for me: Sorry, try again. (3 times) and: [sudo] password for me: sudo: 3 incorrect password attempts Naturally the password is correct
    – bed
    Apr 5, 2020 at 15:33

2 Answers 2

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You should be able to use the -S flag to pipe your password to sudo like this:

pdsh -w me@node[0-3] echo "password" | sudo -S apt update

where password is your actual password.

Also, you can prevent your password from showing up in your ~/.bash_history by placing the following line in your ~/.bashrc file: 

export HISTIGNORE='*sudo -S*'

and don't forget to source your ~/.bashrc file to apply the changes:

source ~/.bashrc

You may need to do this on all machines.

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1
  • Sorry... well there is something strange, if: pdsh -w me@node[0-3] echo "password" | sudo -S apt update the results is: [sudo] password for me: Sorry, try again. [sudo] password for bed: Sorry, try again. [sudo] password for bed: sudo: 3 incorrect password attempts as an incorrect password, but isn't :-/ I have read a similar solution (stackoverflow.com/questions/21659637/…) but for a ssh problem
    – bed
    Apr 10, 2020 at 17:37
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Running on Red Hat, I run commands that require elevated privileges like this:

sudo /usr/local/bin/pdsh -w node[n-m] ?command

This should work as long as root has ssh access to other nodes.

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