$ Linux Command

Processes

pstree

Display a tree of running processes.

processestreehierarchyparentchildren

Additional Notes

pstree displays running processes as a tree structure, showing parent-child relationships. The root of the tree is typically systemd (or init on older systems), with branches showing spawned child processes and threads.

The tree view makes it easy to understand process hierarchies at a glance. It reveals which processes launched which others, helps identify orphaned processes, and shows the structure of complex applications like web servers and container runtimes that fork many children.

Syntax

pstree [options] [pid-or-user]

Parameters

  • pid-or-user: Show the tree starting from a specific PID, or show all trees for processes owned by a specific user.

Common Options

  • -p, --show-pids: Show PIDs in addition to process names.
  • -n, --numeric-sort: Sort output by PID number instead of alphabetically.
  • -a, --arguments: Show command-line arguments.
  • -A: Use ASCII characters for tree drawing.
  • -G: Use VT100 line-drawing characters.
  • -U: Use UTF-8 (Unicode) line-drawing characters.
  • -h, --highlight-all: Highlight the current process and its ancestors.
  • -H pid: Highlight the specified PID and its ancestors.
  • -l, --long: Do not truncate long lines.
  • -s, --show-parents: Show parent processes of the specified PID.
  • -S, --ns-changes: Show namespace changes (useful for containers).
  • -t, --thread-names: Show thread names.
  • -T, --hide-threads: Hide threads (show only processes).
  • -u, --uid-changes: Show UID transitions.
  • -Z, --security-context: Show SELinux security context.
  • -g: Show process group IDs.
  • -c: Disable compact mode (shows all children separately).
  • --color: Colorize output by process age or attributes.

Examples

pstree

Show the full process tree.

pstree -p

Show process tree with PIDs.

pstree -a

Show process tree with command-line arguments.

pstree -p 1234

Show the tree rooted at PID 1234.

pstree username

Show all processes owned by a specific user.

pstree -pan 1

Show the full tree from init/systemd with PIDs and arguments, sorted numerically.

pstree -s 1234

Show only the parent chain of PID 1234.

pstree -S $(pidof docker)

Show process tree with namespace changes for Docker.

pstree -p -h 1234

Show the tree and highlight PID 1234.

Practical Notes

  • The process tree starts at PID 1 (systemd or init). Zombie and orphaned processes appear without proper parents.
  • Use pstree -p when you need to find a specific PID. Pipe to grep for searching.
  • Threads are shown inside curly braces {thread_name}. Use -T to hide threads.
  • The -s option is useful for finding the parent chain of a problematic process.
  • For containers, -S shows which processes are in different namespaces, helping identify container boundaries.
  • pstree is part of the psmisc package (ps, pstree, killall, fuser, prtstat).