Python OSError: [Errno 2]

Question

I have the following code that is attempting to start each of the "commands" below in Linux. The module attempts to keep each of the 2 commands running if either should crash for whatever reason.

#!/usr/bin/env python
import subprocess

commands = [ ["screen -dmS RealmD top"], ["screen -DmS RealmD top -d 5"] ]
programs = [ subprocess.Popen(c) for c in commands ]
while True:
    for i in range(len(programs)):
        if programs[i].returncode is None:
            continue # still running
        else:
            # restart this one
            programs[i]= subprocess.Popen(commands[i])
        time.sleep(1.0)

Upon executing the code the following exception is thrown:

Traceback (most recent call last):
  File "./marp.py", line 82, in <module>
    programs = [ subprocess.Popen(c) for c in commands ]
  File "/usr/lib/python2.6/subprocess.py", line 595, in __init__
    errread, errwrite)
  File "/usr/lib/python2.6/subprocess.py", line 1092, in _execute_child
    raise child_exception
OSError: [Errno 2] No such file or directory

I think I'm missing something obvious, can anyone see what's wrong with the code above?

you should use programs[i].poll() instead of programs[i].returncode. — jfs
– jfs, Commented Nov 22, 2012 at 16:02

sth · Accepted Answer · 2019-03-10 16:39:52Z

66

Use ["screen", "-dmS", "RealmD", "top"] instead of ["screen -dmS RealmD top"].

Maybe also use the complete path to screen.

edited Mar 10, 2019 at 16:39

answered May 23, 2009 at 17:31

sth

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6 Comments

Colin Burnett Over a year ago

Docs say a string or a sequence can be used.

Caedis Over a year ago

commands = [ ["screen", "-dmS", "RealmD", "top"], ["screen", "-DmS", "RealmD", "top", "-d", "5"] ] Worked perfectly!

sth Over a year ago

@colin: In this case a sequence was used and it needs to contain the parameters separately. Probably a simple string (without the []) would also work.

S.Lott Over a year ago

Either 1 string, or 1 parameter "word" per element of a list. If you pass a sequence, you should have done the exact parsing that a shell normally does. If you pass a single string it's parsed exactly the way the shell would have parsed it.

jfs Over a year ago

@umpirsky: from the docs: "On Unix, if args is a string, the string is interpreted as the name or path of the program to execute. However, this can only be done _if not passing arguments to the program_."

|

Colin Burnett · Accepted Answer · 2009-05-23 17:29:51Z

9

Only guess is that it can't find screen. Try /usr/bin/screen or whatever which screen gives you.

answered May 23, 2009 at 17:29

Colin Burnett

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1 Comment

Brian Moeskau Over a year ago

Yep, this was my issue. Command was not in system path as expected.

kirbyfan64sos · Accepted Answer · 2015-01-20 19:14:37Z

7

The problem is that your command should be split. subprocces requires that the cmd is a list, not a string. It shouldn't be:

subprocess.call('''awk 'BEGIN {FS="\t";OFS="\n"} {a[$1]=a [$1] OFS $2 FS $3 FS $4} END
{for (i in a) {print i a[i]}}' 2_lcsorted.txt > 2_locus_2.txt''')

That won't work. If you feed subprocess a string, it assumes that that is the path to the command you want to execute. The command needs to be a list. Check out http://www.gossamer-threads.com/lists/python/python/724330. Also, because you're using file redirection, you should use subprocess.call(cmd, shell=True). You can also use shlex.

edited Jan 20, 2015 at 19:14

answered Mar 7, 2013 at 22:05

kirbyfan64sos

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2 Comments

WoJ Over a year ago

subprocess.call("executable -parameter 1 -hello", shell=True) works (assuming it is in the PATH of the shell)

WoJ Over a year ago

It depends on the call. If you do not parse input then it is as safe as a shell command.

tejaswini teju · Accepted Answer · 2017-05-29 09:10:59Z

3

I got same error when i wrote like this :-

subprocess.Popen("ls" ,shell = False , stdout = subprocess.PIPE ,stderr = subprocess.PIPE)

And problem is solved when i made shell=True .It will work

subprocess.Popen("ls" ,shell = False , stdout = subprocess.PIPE ,stderr = subprocess.PIPE, shell=True)

edited May 29, 2017 at 9:10

answered Apr 15, 2017 at 19:52

tejaswini teju

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Comments

Dennis Williamson · Accepted Answer · 2013-06-12 13:21:50Z

2

commands = [ "screen -dmS RealmD top", "screen -DmS RealmD top -d 5" ]
programs = [ subprocess.Popen(c.split()) for c in commands ]

answered Jun 12, 2013 at 13:21

Dennis Williamson

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1 Comment

Tanky Woo Over a year ago

Use shlex.split() instead of string.split()

Delphine · Accepted Answer · 2016-11-29 15:36:06Z

Just in case.. I also got stuck with this error and the issue was that my files were in DOS instead of UNIX so at :

 return subprocess.call(lst_exp)

where lst_exp is a list of args, one of them was "not found" because it was in DOS instead of UNIX but error thrown was the same :

File "/var/www/run_verifier.py", line 59, in main
return subprocess.call(lst_exp)
File "/usr/lib/python2.7/subprocess.py", line 522, in call
return Popen(*popenargs, **kwargs).wait()
File "/usr/lib/python2.7/subprocess.py", line 710, in __init__
errread, errwrite)
File "/usr/lib/python2.7/subprocess.py", line 1335, in _execute_child
raise child_exception
OSError: [Errno 2] No such file or directory

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