JDB Debugging via tmux

Name: jdb-debugging
Rating: 76
Author: markus1189

Debug running JVM applications using jdb controlled through tmux panes.

Setup

With dedicated pane (preferred): User provides pane ID (e.g., %265)

bash

tmux send-keys -t %265 "jdb -attach PORT" Enter
sleep 2
tmux capture-pane -t %265 -p

With new session:

bash

tmux new-session -d -s jdb "jdb -attach PORT"
sleep 2
tmux capture-pane -t jdb -p

Commands

All commands follow this pattern:

bash

tmux send-keys -t PANE "COMMAND" Enter
sleep 0.5
tmux capture-pane -t PANE -p

Breakpoints

bash

# Simple method (non-overloaded)
stop in com.example.MyClass.myMethod

# Overloaded method - first list methods to find signature
methods com.example.MyClass
# Then use exact signature
stop in com.example.MyClass.execute(java.lang.Object)

# Line breakpoint (often fails with Scala due to line mismatch)
stop at com.example.MyClass:42

Navigation

Command	Action
`cont`	Continue execution
`step`	Step into
`next`	Step over
`step up`	Step out of current method

Inspection

Command	Action
`where`	Stack trace
`locals`	Local variables
`print varName`	Print variable value
`print obj.field`	Print object field
`threads`	List all threads
`thread THREAD_ID`	Switch to thread

Breakpoint Management

Command	Action
`clear`	List breakpoints
`clear com.example.MyClass.myMethod`	Remove breakpoint

Scala/Kotlin Notes

•Line breakpoints often fail - use method breakpoints instead
•For overloaded methods, use methods ClassName to find exact JVM signature
•list command typically fails (source not found) but inspection commands work fine

Cleanup

bash

# Session approach
tmux kill-session -t jdb

# Pane approach - just exit jdb
tmux send-keys -t %265 "quit" Enter