swap – establish a swap file
establishes a file for the system to swap on.
is an existing file, it is used for system swap. If it
does not exist, a new file is created. If
is a directory, a unique file is created in that directory
on which to swap.
The environment variable
is set to the full name of the resulting file.
The number of blocks available in the file or device
must be at least the number of swap blocks configured
at system boot time.
If a swap channel has already been set and no blocks
are currently valid in the file the old file will be
closed and then replaced. If any blocks are valid on
the device an error is returned instead.
Swapping to a file served by a local user-level process
will lead to deadlock if the process isn’t made non-swappable