$ Linux Command

Network

pssh

Parallel SSH for executing commands on multiple hosts.

sshparallelremoteexecutionclusteradministration

Additional Notes

pssh (Parallel SSH) runs SSH commands on multiple remote hosts simultaneously. It connects to a list of hosts, executes a command on each, and collects the output. Results are displayed as each host completes, optionally organized by host.

pssh is invaluable for system administrators managing multiple servers. Common uses include deploying configuration files, checking system status across a fleet, running package updates, restarting services, and gathering logs from many machines. The pssh suite includes several companion tools: pscp (parallel copy), prsync (parallel rsync), pnuke (parallel kill), and pslurp (parallel download).

Syntax

pssh [options] command

Parameters

  • command: The command to run on each remote host.

Common Options

  • -h file, --hosts file: Read hostnames from a file (one per line).
  • -H host, --host host: Specify a single host. Can be used multiple times.
  • -l user, --user user: SSH username for all hosts.
  • -p N, --par N: Run N SSH processes in parallel (default 32).
  • -o dir, --outdir dir: Save standard output of each host to files in this directory.
  • -e dir, --errdir dir: Save error output of each host to files in this directory.
  • -i: Display standard output and error for each host inline.
  • -t timeout, --timeout timeout: Set connection timeout in seconds.
  • -x options, --extra-args options: Pass extra SSH command-line options.
  • -X option: Pass a single SSH option.
  • -O option=value: Set an SSH configuration option.
  • -A, --askpass: Prompt for a password (use SSH keys instead when possible).
  • -I, --inline: Read input from stdin and send it to each ssh process.
  • -v, --verbose: Verbose output.
  • --hosts-file file: Alternate name for -h.

Examples

pssh -h hosts.txt "uptime"

Run uptime on all hosts listed in hosts.txt.

pssh -H web1.example.com -H web2.example.com "systemctl status nginx"

Check nginx status on two web servers.

pssh -h servers.txt -l root -i "df -h"

Run df -h as root on all servers with output shown inline.

pssh -h hosts.txt -o /tmp/output "uname -r"

Save kernel version output for each host to /tmp/output/.

pscp -h hosts.txt /etc/hosts /etc/hosts

Copy /etc/hosts to all hosts in parallel.

pnuke -h hosts.txt nginx

Kill all nginx processes on all hosts in parallel.

prsync -h hosts.txt -l /etc/nginx/ /etc/nginx/

Synchronize the nginx configuration directory to all hosts.

pssh -h servers.txt -t 10 "apt update && apt upgrade -y"

Run package updates with a 10-second timeout per host.

Practical Notes

  • Use SSH key-based authentication for passwordless operation. Set pssh will prompt for passwords with -A, but keys are strongly preferred.
  • The host file format is one host per line, optionally with :port suffix (e.g., server.example.com:2222).
  • Control the parallelism with -p. Start with -p 10 for network-friendly behavior and increase as needed.
  • Output files in -o are named by hostname. Combine with grep to search across results: grep -l "error" /tmp/output/*.
  • pssh is also known as parallel-ssh. Install with sudo apt install pssh on Debian/Ubuntu.
  • For modern alternatives, consider ansible (push-based configuration management), pdsh (parallel distributed shell), or clusterssh (interactive multi-terminal).
  • The environment variable PSSH_NODENUM is set in each parallel process, allowing per-host index-based logic.