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My Raspberry Pi B+ has started to freeze randomly for a few seconds only to continue as if nothing has happened.

I'm connecting over SSH only (no keyboard/monitor) and at least once a minute it will freeze for about 10-60 seconds.

I already have

  • reinstalled the OS (now Linux raspy 3.18.13+)
  • disconnected everything (only power/ethernet remain)
  • changed the power adapter
  • downgraded/upgraded the firmware

Is there anything else that could be the problem?

Update:

  • Ping sometimes times out while it is unresponsive
  • No messages in /var/log/syslog and dmesg
  • trying different firmwares (with rpi-update) had no effect.
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  • 2
    Are you running something that is CPU/memory intensive?
    – Steve Robillard
    May 14, 2015 at 22:28
  • No, it's a fresh system with nothing on it.
    – laktak
    May 14, 2015 at 22:36
  • 2
    You say you have changed the power supply, but have you actually measured the voltage elinux.org/R-Pi_Troubleshooting#Troubleshooting_power_problems
    – Steve Robillard
    May 14, 2015 at 23:02
  • Try keeping 'top', 'ping', and 'watch "dmesg | tail" ' running to see if anything changes during or after the freeze.
    – user1133275
    May 15, 2015 at 0:26
  • Can you try keyboard and mouse with no network? I ask because the Pi has 10/100Mbit/s Ethernet and that can easily become saturated.
    – rob
    May 15, 2015 at 7:20

3 Answers 3

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Your I/O could do such things. For example, if your SD card is slow and you start to do some writes, then your Linux session may be slow to process commands. You will still be able to type commands, but execution may be delayed for several seconds during heavy writes.

In this case, if you have a slow SD card (Class 4 or slower), then I would try to upgrade to Class 10 and see if that will help.

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  • It's already a class 10. But how could I find out if it's hanging because of IO? Is there a tool?
    – laktak
    May 15, 2015 at 20:50
  • You can install atop, which also logs system stats. You can then Analyse tbose after a Freese. Atop's man page tells you how you do that.
    – der_do
    May 15, 2015 at 22:53
  • The simplest way to check is to open a simple editor and see if the cursor moves fine while those "freeze ups". If it does, then your I/O is hitting hard. If your cursor freezes up too, that's something with network connectivity or CPU. I would try to perform the test locally to remove network out of picture.
    – nochkin
    May 16, 2015 at 3:15
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If it's a fresh install (without any firewall) check if you are not victim of a brut force attack by typing :

sudo tail -f /var/log/auth.log

If you see something like

May 10 06:25:12 raspberrypi sshd[26518]: Failed password for root from XX.XX.XX.XX port XXXX ssh2

then you should consider configure iptables and fail2ban...

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  • Thanks for the tip, I hadn't thought of that. Unfortunately after closing ssh from outside and reinstalling the OS the issue still persists.
    – laktak
    Jun 16, 2015 at 19:42
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I discovered I actually had two issues:

  • slow when connecting to the Pi, this was solved by adding UseDNS no to /etc/ssh/sshd_config

  • freeze during ssh - I had less issues after reinstalling the OS but after upgrading to jessie the freezes disappeared completely

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