Today I found my proftpd, which worked just fine for the last 6 months, now does something weird. This weirdness manifests itself in extremely slow transfers - a folder that should take less than a minute now takes an hour! HOWEVER, the actual data transfers still move at expected speeds, when they move - it's just that there are loong gaps between bursts of data! From the client's end, it also takes much longer than usual to log in, or to change directory.
- I tried to use ftp client on another machine, with the same result. I conclude the problem is on the server, and not the LAN, or the client machine.
- I checked the server does not run some other process gobbling the resources - it doesn't, top shows the system at least 90% idle at all times.
- I thought mybe something went wrong with disk access - but no, hdparm shows DMA is on, apps launch and the desktop functions as usual
- I tried to copy the same folder using rsync, rather than ftp client. This worked as it should, at full speed. I conclude both network and the HD on the server are fine.
- I tried to look for some relevant entries in error logs, with no success. I'm not sure where to look though. Proftpd itself doesn't seem to generate any logs...
I'm out of ideas at this point. Help?
Edit: I've been running regular pacman -Syu, the system is current as of last night...
Use tcpdump to see if it's trying reverse DNS lookups and timing out. I've had DNS slow down SSH logins, etc. Wrong /etc/resolv.conf or missing /etc/hosts entries?
The problem was indeed /etc/hosts ... over time it somehow drifted out of sync with reality All is well now, thank you!