问题:

When we launch an instance from an AMI. At first the instance is accessible(ssh). Once we stop/start the instance or reboot it the machine becomes inaccessible via ssh,we can ping it though. We see below error in System log.

AMI ID used - ami-72dc9220 Instance - i-0896a15f -   Linux rhel6.4 M1.large instance. ../  ******************* BLKFRONT for device/vbd/2049 ********** backend at /local/domain/0/backend/vbd/236/2049 Failed to read /local/domain/0/backend/vbd/236/2049/feature-barrier. Failed to read /local/domain/0/backend/vbd/236/2049/feature-flush-cache. 14680064 sectors of 512 bytes ************************** Thread "kbdfront": pointer: 0x21e0130010, stack: 0x3720000 FBFRONT for device/vfb/0 ********** KBDFRONT for device/vkbd/0 ********** Failed to read device/vfb/0/backend-id. Failed to read device/vkbd/0/backend-id. Error ENOENT when reading the backend path device/vkbd/0/backend Thread "kbdfront" exited. Error ENOENT when reading the backend path device/vfb/0/backend  ./

回答1:

Was able to fix this. This is due to a bug from REDHAT for 6.4 rhel instances. After launching the machine from an AMI, connect to the machine and switch to root user and make below changes to /etc/rc.d/rc.local file ...

Remove the following three lines and save the file:

cat <<EOL >> /etc/ssh/sshd_config  UseDNS no  PermitRootLogin without-password ../

One should also remove garbage entries from /etc/ssh/sshd_config file.

The machine once rebooted after these changes works fine.

回答2:

Also comment following lines in /etc/ssh/sshd_config

permitrootlogin without-password permitrootlogin without-passwordUseDNS no

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