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Date: Sat, 21 Feb 2015 12:11:57 +1100
From: Cameron Simpson <cs@zip.com.au>
To: python-list@python.org
Subject: Re: subprocess command fails
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On 20Feb2015 15:30, Brad s <bcddd214@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 soluti=
on 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 y=
our=20
question and give some background first, then list offending output with a=
=20
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 test1=
23.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 =3D subprocess.call(['dnssec-signzone','-e',strftime('%Y%m%d%H', gm=
time())+'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 comm=
and=20
line. FOr example, your shell command line supplied the -e optin as=20
"-e20180330000000", but your python code generates two strings: "-e",=20
"20180330000000".

It may not matter, but it is not identically worded and some commands are p=
icky=20
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 =3D [ 'dnssec-signzone',
                  '-e', strftime('%Y%m%d%H', gmtime())+'0000',
                  '-p',=20
                  '-t',
                  '-g',
                  '-k', zcombined+'.ksk.key',
                  '-o', dname,
                  dname+'.external',
                  zcombined+'.zsk.key'
                ]
      print("command =3D %r" % (cmdargv,))
      sfmove =3D 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=20
reproduce the error. Then debug on the command line. Then fix the python co=
de=20
accordingly.

>#cmd =3D "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 coma=
nd=20
=66rom some input line obtained from a user. Stick with your current "const=
ruct a=20
list" approach: more robust.

I notice your code removes a bunch of files. Might it remove a necessary fi=
le=20
for the command?

Cheers,
Cameron Simpson <cs@zip.com.au>