You're hitting a quoting problem; the $5 is being interpreted at the wrong time. There are at least two solutions:

1. Put a \ before the $; e.g.

   /usr/bin/ssh -i /path/to/key user@server "df -h | grep /dev/root | awk '{print \$5}'"

2. Run the df remotely but the grep and awk locally. e.g.

   /usr/bin/ssh -i /path/to/key user@server df -h | grep /dev/root | awk '{print $5}'

FWIW, I'd run a version of the second option but merging grep and awk

/usr/bin/ssh -i /path/to/key user@server df -h | awk '/\/dev\/root/ {print $5}'

You're hitting a quoting problem; the $5 is being interpreted at the wrong time. There are at least two solutions:

1. Put a \ before the $; e.g.

   /usr/bin/ssh -i /path/to/key user@server "df -h | grep /dev/root | awk '{print \$5}'"
   

2. Run the df remotely but the grep and awk locally. e.g.

   /usr/bin/ssh -i /path/to/key user@server df -h | grep /dev/root | awk '{print $5}'
   

FWIW, I'd run a version of the second option but merging grep and awk

/usr/bin/ssh -i /path/to/key user@server df -h | awk '/\/dev\/root/ {print $5}'

You're hitting a quoting problem; the $5 is being interpreted at the wrong time. There are at least two solutions:

1. Put a \ before the $; e.g.

/usr/bin/ssh -i /path/to/key user@server "df -h | grep /dev/root | awk '{print \$5}'"

1. Run the df remotely but the grep and awk locally. e.g.

/usr/bin/ssh -i /path/to/key user@server df -h | grep /dev/root | awk '{print $5}'

FWIW, I'd run a version of the second option but merging grep and awk

/usr/bin/ssh -i /path/to/key user@server df -h | awk '/\/dev\/root/ {print $5}'

You're hitting a quoting problem; the $5 is being interpreted at the wrong time. There are at least two solutions:

1. Put a \ before the $; e.g.

   /usr/bin/ssh -i /path/to/key user@server "df -h | grep /dev/root | awk '{print \$5}'"

2. Run the df remotely but the grep and awk locally. e.g.

   /usr/bin/ssh -i /path/to/key user@server df -h | grep /dev/root | awk '{print $5}'

FWIW, I'd run a version of the second option but merging grep and awk

/usr/bin/ssh -i /path/to/key user@server df -h | awk '/\/dev\/root/ {print $5}'