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My server is often almost DOS'ed by crawlers. I have not yet managed to figure out what exactly is responsible for the high load. CPU, memory and disk IO are not at the limit (could be network traffic). My question is, if anyone has an idea how to reserve capacity in the system to run a shell session (bash over ssh). Can this be done using cgroups? Right now load values easily go up to 60 and that make it hard to enter any command.

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ulatencyd could be of use here, I've never tried it, though... – sr_ Aug 14 '12 at 11:00
that looks interesting. will report back later. Thanks! – ensonic Aug 14 '12 at 11:51

Something more basic: start sshd on a specific port with a very low nice level, which might help.

# nice -20 /usr/sbin/sshd -p 2222 

IF the problem is due to DOS throttling the network, then you have to use network-shaping rules outside the box (ie, on the switch).

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