differential / incremental backup - How to specifiy ?

You need to create a schedule that has full marked on a day and then you select level 1-9 (Diff.) OR Incr. based on your choice.

If you want this schedule for a clinet in a group, you set this as schedule for the client and if you want to set it for all the clients of the group, select this schedule for the group. Run gorup with savegrp as you normally do, it would work with new schedule.

Run savegrp -G groupname, it would use group/client scheduler.

Create a schedule within networker. Name it test for exemple.
For a differential backup use only 1 level.

After in your external scheduler use the following command

savegrp -C test yourgroupname

You don't need to create a new group. Specify level from CLI when calling group by feeding -l option which stands for level. Check savegrp manual. That might be handy if your scheduling solution is such that you can feed switch to command you call based on day or whatever would be your trigger for specific level.

Why would you avoid bootstrap backup? Anyway,-I should do the trick. If you see bootstrap backup you will see that only with groups where you have server client. as of 7.3.x you can't skip bootstrap as before. Of course, to skip bootstrap in other groups you must have backup server client in active group.

Savegrp command is not the solution beacuse it will forece all the clients will force to have the same vel and we use the skip level to avoid to backup the boostrap.
root@sisley[]# savegrp -I -n -l 1 -vvv HSYS1
sys1:/ level=1
sys1:/mount/fs/fs1 level=1

* If the HSYS1 use level 1 , it doesn't work because the client's schedule field override the group level property.

I haven't found yet the solution.

I think you should create shcedules and use them on respective clients. Don't use a schedule on the group. Start the group using savegrp OR GUI as you want to and NW would use the client's schedule.

Why would you like to skip Bootstrap backup?