Under Linux, the usual fortran compiler, f77, is unavailable. The command "f77" is actually a symbolic link to the GNU Fortran compiler, g77.
IF you wish, you can also use the f77 compiler from the Sunsoft locker. Because 'f77" is installed locally and is in your $PATH, you must use the "-f" option to "add" when adding the locker.
There may be very slight differences between GNU Fortran and traditional Fortran 77, but most code should work.