subprocess command fails

[Cameron Simpson]

On 20Feb2015 15:30, Brad s <bcddd214 at gmail.com> wrote:
>I am trying to execute a subprocess, something done in my script a couple of times. But on the last one, it outputs an error I cannot find the solution to.  The exact same command using the same files produced at the command line works just fine.
>

Hi Brad,

I have reordered your post in my quote for readability. It is best to ask your 
question and give some background first, then list offending output with a 
description of good output, then the code.

You write:

>The first command works on the command line:
>
>dnssec-signzone -e20180330000000 -p -t -g -k Ktest123.com.ksk.key -o test123.com test123.com.external Ktest123.com.zsk.key
>Verifying the zone using the following algorithms: RSASHA256.
>Zone fully signed:
>Algorithm: RSASHA256: KSKs: 1 active, 0 stand-by, 0 revoked
>                      ZSKs: 1 active, 0 stand-by, 0 revoked
>test123.com.external.signed
>Signatures generated:                        9
>Signatures retained:                         0
>Signatures dropped:                          0
>Signatures successfully verified:            0
>Signatures unsuccessfully verified:          0
>Signing time in seconds:                 0.010
>Signatures per second:                 875.401
>Runtime in seconds:                      0.013

Which is excellent.

Then you supply your code:

>sfmove = subprocess.call(['dnssec-signzone','-e',strftime('%Y%m%d%H', gmtime())+'0000','-p','-t','-g','-k',zcombined+'.ksk.key','-o',dname,dname+'.external',zcombined+'.zsk.key'])

I would start by pointing out that this is not identical to your shell command 
line. FOr example, your shell command line supplied the -e optin as 
"-e20180330000000", but your python code generates two strings: "-e", 
"20180330000000".

It may not matter, but it is not identically worded and some commands are picky 
about this kind of thing.

For debugging purposes I would do two things:

- compute the python command argument list as a separate list and print it out, example:

      cmdargv = [ 'dnssec-signzone',
                  '-e', strftime('%Y%m%d%H', gmtime())+'0000',
                  '-p', 
                  '-t',
                  '-g',
                  '-k', zcombined+'.ksk.key',
                  '-o', dname,
                  dname+'.external',
                  zcombined+'.zsk.key'
                ]
      print("command = %r" % (cmdargv,))
      sfmove = subprocess.call(cmdargv)

  Note the use of %r to print the contents of the command clearly.
  (BTW, "sfmove"? Surely "sign" or something.)

- hand run _exactly_ the command printed out by the print call above

If you run _exactly_ what your python comman did, you should be able to 
reproduce the error. Then debug on the command line. Then fix the python code 
accordingly.

>#cmd = "dnssec-signzone','-e',strftime('%Y%m%d%H', gmtime())+'0000','-p','-t','-g','-k','K'+dname+'.ksk.key','-o',dname,dname+'.external','K"+dname+'.zsk.key'
>#subprocess.check_call(shlex.split(cmd))

Remark: shlex.split is not a good way to make a command line unless it comand 
from some input line obtained from a user. Stick with your current "construct a 
list" approach: more robust.

I notice your code removes a bunch of files. Might it remove a necessary file 
for the command?

Cheers,
Cameron Simpson <cs at zip.com.au>