What determines the current working directory of Tomcat Java process?

Question

My production server runs Linux using System V style init scripts.

Tomcat is brought up by running service tomcat6 start as root user (service runs init script under cwd /).

Tomcat then serves a web page to write the result of new File(".").getAbsolutePath(), which shows /usr/share/tomcat6/.

But Tomcat init script (/etc/init.d/tomcat6) makes no mention of CWD, neither does it have any cd command.

Given that Java itself cannot change current working directory, then how come /usr/share/tomcat6 became Tomcat's current working directory? Where in its startup process changes its cwd?

The Linux in question is CentOS6.

Solution

On CentOS 6, the Tomcat init.d script launches tomcat by means of this line:

$SU - $TOMCAT_USER -c "${TOMCAT_SCRIPT} start-security"

$SU is either /bin/runuser or /bin/su, $TOMCAT_USER is normally "tomcat", and $TOMCAT_SCRIPT is normally "/usr/sbin/tomcat6". "su -" or "runuser -" runs its command as the specified user, from the specified user's home directory. So this command will change to the "tomcat" user's ID and home directory, then run /usr/sbin/tomcat6. The tomcat6 script eventually launches tomcat itself.

The tomcat user's home directory should be the same as CATALINA_BASE. In short, the "su" or "runuser" command here is what sets the current working directory to CATALINA_BASE.

The init.d script isn't formally part of tomcat; it's supplied by the package maintainer, and it can be different from one system to another. On my Ubuntu 13 system, /etc/init.d/tomcat6 contains a command to cd to $CATALINA_BASE.

Tomcat's own startup scripts (bin/startup.sh and so on) don't set a working directory. When I launch tomcat 6 or tomcat 7 directly using its own startup script, it just inherits the working directory that I ran it from.

Remember that on Linux, you can see any process's actual current directory by checking /proc/<pid>/cwd.

Comments

[Admin]

I've certainly seen those env variables, but have not seen cd $CATALINA_HOME.

[Admin]

Awesome. I just noticed that /etc/passwd defines tomcat user home directory as /usr/share/tomcat6.