JDB Debugging via tmux

Debug running JVM applications using jdb controlled through tmux panes.

Setup

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

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

With new session:

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

Commands

All commands follow this pattern:

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

Breakpoints

# 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

# Session approach
tmux kill-session -t jdb

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