Why does the linux server periodically fall off?

Question

linux

Welcome all.

There is a mail server on Debian, which, after stable operation for several years, began to "fall off" several times a day for 5-7 minutes. It looks like this: any web interface of the server (for example, Roundcube) stops opening ("cannot connect to the server"), when you try to connect via putty via ssh - just a black connection window hangs without an authorization prompt, but there is no error like "network error connection" does not pop up. At the same time, the server is pinged to everything, there is no packet loss. After 5-7 minutes of "dumping" the previous performance itself is restored. I looked at the

mysql, apache2, error and syslog logs - emptiness or nothing suspicious.

With what such glitches can be connected? What else can be used for diagnosis?

Answer 1

1. Check SMART hard drives.
2. Connect monitoring and check for incomprehensible bursts of IO\CPU\RAM.
3. Check the channel load for the same incomprehensible bursts of traffic.
3. If you do not have server support from the OS - updates, firewall, etc. (and it is logical to assume that if it were, no questions would be asked here) - it means that the server is probably hacked and used by someone, which causes loads. Or just DDOS arrives from somewhere.

Answer 2

See the kernel log (dmesg). It is possible that the conntrack table is overflowing or something like that.