A thread dump is a list of all the Java threads that are currently active in a Java Virtual Machine (JVM). There are several ways to take thread dumps from a JVM. It is highly recommended to take more than 1 thread dump while analyzing any problem such as deadlock or resource usage analysis. It is always better to confirm in more than one thread dump then making conclusions in single attempt.
1. Get the PID of Java process
The first piece of information you will need to be able to obtain a thread dump is your java process’s PID.
The java JDK ships with the jps command which lists all java process ids. You can run this command like this:
$ jps -l
Remember – you may have to run this command as $ sudo -u jps -l, where “user” is the username of the user that the java process is running as.
Even now, if you are not able to find out process id, use below command:
$ ps -aef | grep java
2. Request a Thread Dump from the JVM
If installed/available, we recommend using the jstack tool. It prints thread dumps to the command line console.
To obtain thread dump using jstack, run the following command:
$ jstack
You can output consecutive thread dumps to a file by using the console output redirect / append directive:
$ jstack >> threaddumps.log
Important points
- The jstack tool is available since JDK 1.5.
- jstack works even if the -Xrs jvm parameter is enabled.
- It’s not possible to use the jstack tool from JDK 1.6 to take threaddumps from a process running on JDK 1.5.
3. Thread dump sampling in fixed time intervals using jstack script
This simple shell script takes several jstack snapshots in fixed time intervals: [Reference document]
#!/bin/bash if [ $# -eq 0 ]; then echo >= 2 "Usage: jstackSeries [ count [ delay ] ]" echo >= 2 " Defaults: count = 10, delay = 1 (seconds)" exit 1 fi pid=$1 # required count=${2:-10} # defaults to 10 times delay=${3:-1} # defaults to 1 second while [ $count -gt 0 ] do jstack $pid >jstack.$pid.$(date +%H%M%S.%N) sleep $delay let count-- echo -n "." done
Use above script like this:
$ jstackSeries 10 5
4. How to compare two JStack thread dumps
To compare thread dumps you may use interactive difference viewers, e.g.
$ vimdiff file1 file2 file3 file4 # up to 4 files
Another way to see what parts of the jstack trace are changing over time is to compare adjacent jstack trace using $ context diff (-c option):
d_old="" for d in jstack.13585.12171* do if [ -n "$d_old" ] then diff -c "$d_old" "$d" fi d_old="$d" done
Here, the result shows only the places where the JStack thread dump changes from file to file.
Happy Learning !!
satish
we have installed java 1.7 but when we use jstack command it is saying as command not found
we need to install jstack package using yum or rpm, also we need to set the JAVA_HOME and PATH
Also if we want to set permanently what is the path
Thanks
chakri
Hi..
My application is running on java 5 and when I tried to run jstack command it is saying command not found.
I searched in /opt/java 1.5/bin folder I couldn’t see any jstack command.
Where as when I see in java 6/bin folder I can see jstack command.
Can you suggest me how to proceed.
Chakri
chakri.950@gmail.com
Lokesh Gupta
you need to upgrade java version.
Prem
PID was missed
jstack pid >>threaddumps.log
Prem
We missed to mention
Prem
Hi
I think this should be the statement.
jstack >> threaddumps.log
pintu
Thanks Dear for sharing such a nice information !!
Vishesh
Great information, dude !!
sayyapillai
Thanks for your grateful informations, am working in FNT software solutions, so it will be helpful info for my works.