Crashplan for Dummies, aka Step by Step :)

Hi
I think I now have successful installed java having found some instructions on p10 of this forum.

java version "1.7.0_65"
OpenJDK Runtime Environment (IcedTea 2.5.1) (7u65-2.5.1-5~deb7u1)
OpenJDK 64-Bit Server VM (build 24.65-b04, mixed mode)

but now when i try to run crashplan install i get the following message

Welcome to the CrashPlan Installer.

Press enter to continue with installation.

Validating environment...
  detected root permissions
mkdir: cannot create directory `./lib': File exists
cpio: unrecognized option '--no-preserve-owner'
BusyBox v1.20.2 (Debian 1:1.20.0-7) multi-call binary.

Usage: cpio [-dmvu] [-F FILE] [-H newc] [-tio] [EXTR_FILE]...

Extract or list files from a cpio archive, or
create an archive using file list on stdin

Main operation mode:
        -t      List
        -i      Extract EXTR_FILEs (or all)
        -o      Create (requires -H newc)
        -d      Make leading directories
        -m      Preserve mtime
        -v      Verbose
        -u      Overwrite
        -F FILE Input (-t,-i,-p) or output (-o) file
        -H newc Archive format

Error: Could not find or load main class com.code42.utils.JavaEnvironment
'/tmp' not writable.

Any suggestions for where I'm going wrong?

thanks