Try using the server with the following script:
#!/bin/sh
java -Xmx2048M -Xms1024M -jar Tekkit.jar nogui
I strongly recommend allocating 2 GB instead of 1. A regular minecraft server nearly 'can't keep up' with 1 GB and the tekkit server has all those mods installed too.
However, if you don't want to allocate that much, use this one:
#!/bin/sh
java -Xmx1024M -Xms512M -jar Tekkit.jar nogui