david@utzoo.UUCP (David Trueman) (09/23/83)
As some people are already aware, most commands on UNIX can be run `in the
background' by putting an ampersand (&) on the end of the command. This
causes the command to start executing as usual, but the user is then allowed
to type more commands without waiting for the `background' command to finish.
One can, for example, submit one file for printing and go on to edit another
file. Another use might be to print a long file and sign off immediately; in
this case, you should use the "nohup" prefix to make sure that the command
will continue to run after you sign off (this is _n_o_t guaranteed otherwise):
nohup ms -p lpr paper &
("Nohup" is short for "no hangup", meaning that the command runs on even if
the user disconnects from the system.)
While this capability can be most useful, it can be (and has been) abused. It
_i_s possible to run several _m_s's or _f_o_r_m_a_t's at the same time in the back-
ground, but there is NO POINT in doing this. Simultaneous _f_o_r_m_a_t's or _m_s's
are actually _s_l_o_w_e_r than they would be if done one at a time, because they
fight each other for system resources. Moreover, this tends to make the sys-
tem intolerably slow for other users. People who do this can expect to be
charged extra -- a lot extra -- for their antisocial habits, and persistent
offenders may lose their Unix accounts altogether. There are (more compli-
cated) ways of doing the same thing without the undesirable side effects; come
see us if you need the details.