What is this?

This knowledgebase contains questions and answers about PRTG Network Monitor and network monitoring in general.

Learn more

PRTG Network Monitor

Intuitive to Use. Easy to manage.
More than 500,000 users rely on Paessler PRTG every day. Find out how you can reduce cost, increase QoS and ease planning, as well.

Free Download

Top Tags

View all Tags

No valid result form SSH Shell



We have recently updated our Synolgy NAS Systems to DSM 5.1.

After this update I had the problem, that my SSH Sensors stopped working.

Error: Server does not support diffie-hellman-group-sha1 for keyexchange.

I fixed that using this: http://blog.millard.org/2014/11/repair-synology-dsm51-for-use-as-linux.html

But now I only get "No valid result from SSH Shell".

I had PRTG create a log for a working SSH Sensor on a different linux machine and the synology one.

This is the synology one:


BusyBox v1.16.1 (2014-11-06 15:59:06 CST) built-in shell (ash)
Enter 'help' for a list of built-in commands.


From the working one on the other machine I could see, that the executed command is this one.

echo PAESSHSTART;df -TP -x tmpfs -x devtmpfs -x debugfs;echo;echo PAESSHEND;exit

I don't know if it's even executed on the synology since the logfile doesn't show that.

But the command also doesn't work, when you type it in an open ssh session, because there is neither a -T nor a -x option for df on this system.

This is what I get, when I try to execute the command manually:

df: invalid option -- 'T'
BusyBox v1.16.1 (2014-11-06 15:59:06 CST) multi-call binary.

Usage: df [-Pkmh] [FILESYSTEM]...

Print filesystem usage statistics

        -P      POSIX output format
        -k      1024-byte blocks (default)
        -m      1M-byte blocks
        -h      Human readable (e.g. 1K 243M 2G)


This is the output of df -P:

Filesystem           1024-blocks    Used Available Capacity Mounted on
/dev/md0               2451064    581960   1766704  25% /
/tmp                    516888       892    515996   0% /tmp
/run                    516888      2548    514340   0% /run
/dev/shm                516888         0    516888   0% /dev/shm
/dev/vg1000/lv       5800273360  55182668 5744988292   1% /volume1

Any way to quickly fix this?

linux prtg ssh synology

Created on Nov 13, 2014 1:47:03 PM

3 Replies



Dear treinhardt

For debug purposes, please enable "Write Result to Disk" and send the respective log file to [email protected]. Please include your question and the information, which of the SSH sensors you use.

Created on Nov 13, 2014 5:07:58 PM by  Arne Seifert [Paessler Support]



Just to add: i have the exact same problem as the topic-starter. I too fixed the diffy-hellmann issue succesfully, but PRTG still returns the error "no valid result from SSH shell". It worked fine in DSM 5.0.x so i can only conclude that Synology "changed something" in 5.1

Created on Nov 27, 2014 1:57:38 PM



Hi treinhardt, stevenrodenburg1,

Thanks for letting us know about this issue.

It looks like PRTG is unable to tell that your target system is indeed running BusyBox. Due to this misconception, it tries to execute the df command with an invalid parameter (as you demonstrated).

Can either of you please execute the command "df --version" on the target machine and show us the output?


Created on Dec 1, 2014 9:58:17 AM by  Yannic Stolz [Paessler Support] (0)

Disclaimer: The information in the Paessler Knowledge Base comes without warranty of any kind. Use at your own risk. Before applying any instructions please exercise proper system administrator housekeeping. You must make sure that a proper backup of all your data is available.