DreamHost does not allow persistent processes to be ran on shared servers. Persistent processes are defined as any UNIX user's command running non-interactively. Basically, something that runs while you aren't actively sitting there interacting with it through a shell window.
DreamHost reserves the right to kill any user process on a shared server without warning or prior notification at the discretion of support or the administrators. This is done to protect other users and maintain the integrity of the shared server.
This is not just done capriciously, however. This is generally done when a process is, in any way, adversely affecting the functionality of a shared server.
Private and dedicated servers
The same policies do not apply to VPS and Dedicated servers. These types of servers can run whatever (LEGAL) processes you like. However, the owner must realize they then accept responsibility for any negative impact this may have on their machine.
What types of processes are forbidden by DreamHost?
Please refer to the Acceptable Use Policy.