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, Nov 22 '12 at 16:02
related: [subprocess.call using string vs using list](http://stackoverflow.com/q/15109665/4279) — jfs, Dec 16 '15 at 18:38

sth · Accepted Answer · 2019-03-10T16:39:52.317

66

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

Maybe also use the complete path to screen.

edited Mar 10 '19 at 16:39

answered May 23 '09 at 17:31

sth

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Docs say a string or a sequence can be used. – Colin Burnett May 23 '09 at 17:44
commands = [ ["screen", "-dmS", "RealmD", "top"], ["screen", "-DmS", "RealmD", "top", "-d", "5"] ] Worked perfectly! – Caedis May 23 '09 at 17:48
@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. – sth May 23 '09 at 18:04
1

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. – S.Lott May 23 '09 at 19:19
@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_."* – jfs Jan 22 '15 at 04:43
How do i use `&` sign? Something like this :- `cmd_list=['dd','if=/dev/zero','of=/dev/null','&']` – mihir6692 Jun 09 '17 at 12:32

score 9 · Answer 2 · answered May 23 '09 at 17:29

9

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

answered May 23 '09 at 17:29

Colin Burnett

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Yep, this was my issue. Command was not in system path as expected. – Brian Moeskau May 07 '18 at 21:38

kirbyfan64sos · Answer 3 · 2015-01-20T19:14:37.050

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 '15 at 19:14

answered Mar 07 '13 at 22:05

kirbyfan64sos

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`subprocess.call("executable -parameter 1 -hello", shell=True)` works (assuming it is in the PATH of the shell) – WoJ Nov 06 '13 at 06:55
It depends on the call. If you do not parse input then it is as safe as a shell command. – WoJ Nov 08 '13 at 10:09

tejaswini teju · Answer 4 · 2017-05-29T09:10:59.450

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 '17 at 09:10

answered Apr 15 '17 at 19:52

tejaswini teju

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score 2 · Answer 5 · answered Jun 12 '13 at 13:21

2

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

answered Jun 12 '13 at 13:21

Dennis Williamson

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Use `shlex.split()` instead of `string.split()` – Tanky Woo Mar 03 '15 at 13:57

score 0 · Answer 6 · answered Nov 29 '16 at 15:36

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

Python OSError: [Errno 2]

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