# 4. Command reference¶

## 4.1. Command line options¶

|Nmag| supports a number of command line options to configure its behaviour.

Suppose the simulation script is called X.py, then these OPTIONS can be specified like this:

nsim X.py OPTIONS


X.py needs to contain at least the line import nmag as this will process the command line options.

The available options are:

–clean:

to override any existing _dat.h5 and _dat.ndt files. If this option is not provided and the data files exist already, then |nmag| will interrupt the execution without having modified the data files on the disk.

Example:

nsim X.py --clean

–loglevel:

this switch determines the amount of information that is being send to stdout (usually the screen) and also to the file X_log.log.

The available levels are in increasing order of detail:

error: print no messages apart from errors print warnings print a moderate amount of information (default) print slightly more information print a lot of information (typically for developer and debugging use)

Example:

nsim X.py --loglevel info2


or:

nsim X.py --loglevel debug

–slavelog:

Log message from slave nodes (when running under MPI) are usually supressed. This switch activates them. Printing these messages will reduce the MPI performance somewhat as the messages are printed to stdout on each slave, and then have to be transferred through the network to the master process.

Note that any log-messages from the nodes will only go to stdout (whereas log messages from the master will also go into the log file, see File names for log files.)

Messages from slave nodes are preceeded by S0X where X is the rank of the node. I.e. log messages from slave node with rank 2, would start with S02.

Example:

nsim X.py --slavelog

–restart:

If a calculation of a hysteresis loop is interrupted (power cut, computer crash, exceeding allocated run time on cluster, etc), then the calculation can be carried out starting from the moment when the last restart file was saved (see Restart example).

This continuation is activated with the --restart switch.

Example:

nsim X.py --restart


Note that this functionality is only available for the hysteresis loop.

The command line options can be combined, for example:

nsim X.py --clean --loglevel debug


There are a few other switches (mostly for debugging) which can be seen using:

nsim X.py --help