Swiss Java Knife (SJK)

[](#swiss-java-knife-sjk)

SJK is a command line tool for JVM diagnostic, troubleshooting and profiling.

SJK exploits standard diagnostic interfaces of JVM (such as JMX, JVM attach and perf counters) and adds some more logic on top useful for common troubleshooting cases. SJK can also be used as a library for building application specific diagnostic tools or to enhance your code with self monitoring features.

What you can do with SJK?

[](#what-you-can-do-with-sjk)

Monitor Java threads in real time
Analyze head dynamics with advanced class histograms
Access MBean attributes and operation from command line
Create flame graphs and over reports from snapshots created VisualVM, Java Flight Recorder or SJK's own sampler

See full command reference.

Download

[](#download)

Latest prebuild binaries

wget https://training.ragozin.info/sjk.jar -> sjk.jar

Starting sjk

[](#starting-sjk)

java -jar sjk.jar <cmd> <arguments>
java -jar sjk.jar --commands
java -jar sjk.jar --help <cmd>

Below a few command from SJK (full command reference).

ttop

[](#ttop)

Pools thread CPU usage of the target JVM and periodically reports to the console.

can attach via PID or open JMX port
displays thread memory allocation rate and cumulative process allocation rate
displays safe point time consumption (only if attache via PID)

More details

hh

[](#hh)

Similar to jmap -histo.

plus can show a histogram of dead objects (histograms of all and live requested, then difference is calculated)
plus can show N top buckets in histogram

More details

stcap, stcpy, ssa and flame

[](#stcap-stcpy-ssa-and-flame)

These commands provide basic sample profiler capabilities. stcap produces hyper-dense stack trace dump (about 1000 compression rate compared to text format) and ssa provides few reports over dump files. stcpy can copy data in archives produced by stcap (e.g. merging dumps or filtering selected threads).

So far following reports are available:

sophisticated filtering (time, stack trace, thread name)
stack frame histogram with advanced filtering options
flame graph visualization (SVG or interactive HTML)
per thread summary (CPU usage, memory allocation, etc)
converting back to text format

Dump file can be also processed programatically.

More details

mx

[](#mx)

This command allows you to do basic operations with MBean from command line.

It can:

read MBean attributes
update MBean writeable attributes
invoke MBean operations (arguments are supported)
display composite and tabular data in a human readable format
use wild cards to shorten MBean names (e.g. *:*,name=CodeCacheManager instead of java.lang:type=MemoryManager,name=CodeCacheManager)
connect to local JVM processes by PID (e.i. any Java process, you do not need to enable JMX server)
connect to JMX using host:port (password authentication is supported)

More details