How to backup "autostart for linux" config ?

What do you exactly mean by Autostart config.?

The autostart databases get mirrored on there on to the other server of the node.

You can backup linux client otherwise by just mentioning the required folders as save sets as we normally do.

In order to backup the Autostart configuration you need to export it to the static file first. You can do it either through the console (by clicking on the domain name at which point the export and import options become available on the toolbar or menu), or through the command line by executing:
$FT_DIR/bin/ftcli -cmd backup

This will create a file called backup.def in the current directory which you can back up and use later to restore your configuration by importing it in the domain.

Remeber that you *should not* back up the "live" cluster database at any time, cluster services require exclusive access to it at all times and you can cause corruption if you try to back it up while cluster is running. The database is located in $FT_DIR/[domainname]_[nodename] directory.

It is all in documentation - please read it and pay attention to ftcli command, especially DOmain Backup chapter.