Java program (class > .jar) as a Unix shell (in place of sh/bash)?

Question

I'm looking to run a Java program (compiled class > .jar file) as my Unix shell. Basically, I don't want sh or bash to be involved, as then users could shell out/suspend out of my Java program and access the unix shell.

Is this possible?

Do I need to use jail/chroot?

Is it as simple as editing /etc/shells and putting the java -jar ... command in there?

Alternatively, if I must use sh/bash, can I auto-exit the shell when my java/vm expires or is unloaded (so nobody can escape the Java app into the bash/sh shell itself)?

that other guy · Accepted Answer · 2014-02-04 23:37:27Z

2

Step one: Create a wrapper shell script /usr/bin/myjavashell:

#!/bin/sh
exec /usr/bin/java -jar /usr/local/whatever/file.jar

Step two: Make it executable: chmod +x /usr/bin/myjavashell

Step three: Add /usr/bin/myjavashell to /etc/shells.

Step four: Set this as the user's login shell with chsh -s /usr/bin/myjavashell youruser.

Optional step five : In /etc/ssh/sshd_config, disable any additional options you don't want the user to be able to do that doesn't require a shell, like tcp forwarding:

Match User youruser
AllowTcpForwarding False

answered Feb 4, 2014 at 23:37

that other guy

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IPvFletch Over a year ago

Thanks 'that other guy' - this is (a more comprehensive description) of what DwB said. Fortunately I've been working with Unix for ~20 years, so after DwB mentioned exec (never had come across that until now!) I could figure the rest out. For others though, and for re-assurance, thank you for your detailed steps, I think this is what I will plan to do. I will still explore the PTY model, as a nifty other alternative (perhaps for future use).

IPvFletch · Accepted Answer · 2014-02-04 21:15:06Z

0

One potential solution I came up with is to make my Java app spawn a PTY and output to the PTY. Then redirect console (vga/serial/vnc/etc) to use my custom PTY. This way the interface is just my Java app's I/O and no bash/shell is ever involved. I think it could work. Need to research how to spawn a PTY and write/read to/from it of course, but I'm sure that is feasible..

Any other ideas?? Thanks!

answered Feb 4, 2014 at 21:15

IPvFletch

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