I am calling this piece of code, but it produces some output in the console where I ran the python script (due to tee command):
os.system("echo 3 | sudo tee /proc/sys/vm/drop_caches")
This version does not produce console output but is there another way?
os.system('sudo bash -c "echo 3 > /proc/sys/vm/drop_caches"')
To hide output of subprocess with Python, we can set stdout to subprocess. DEVNULL`. to output the echo command's output to dev null by setting the stdout to subprocess. DEVNULL when we call subprocess.
An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs.
To answer the question based on its title in the most generic form:
To suppress all output from os.system()
, append >/dev/null 2>&1
to the shell command, which silences both stdout and stderr; e.g.:
import os
os.system('echo 3 | sudo tee /proc/sys/vm/drop_caches >/dev/null 2>&1')
Note that os.system()
by design passes output from the calling process' stdout and stderr streams through to the console (terminal) - your Python code never sees them.
Also, os.system()
does not raise an exception if the shell command fails and instead returns an exit code; note that it takes additional work to extract the shell command's true exit code: you need to extract the high byte from the 16-bit value returned, by applying >> 8
(although you can rely on a return value other than 0
implying an error condition).
Given the above limitations of os.system()
, it is generally worthwhile to use the functions in the subprocess
module instead:
For instance, subprocess.check_output()
could be used as follows:
import subprocess
subprocess.check_output('echo 3 | sudo tee /proc/sys/vm/drop_caches', shell=True)
The above will:
stderr=subprocess.STDOUT
as an additional argument would also capture stderr.Note: Python 3.5 introduced subprocess.run()
, a more flexible successor to both os.system()
and subprocess.check_output()
- see https://docs.python.org/3.5/library/subprocess.html#using-the-subprocess-module
Note:
tee
in the first place - despite not being interested in stdout output - is that a naïve attempt to use > ...
instead would be interpreted before sudo
is invoked, and thus fail, because the required privileges to write to /proc/sys/...
haven't been granted yet.os.system()
or a subprocess
function, stdin is not affected by default, so if you're invoking your script from a terminal, you'll get an interactive password prompt when the sudo
command is encountered (unless the credentials have been cached).Write directly to the proc pseudo file instead via Python i/o lib.
This will require your script to run as root (via sudo
), which means you should limit its scope to being an admin only tool. This also allows the script to run on boxes where sudo
requires a password.
Example:
with open("/proc/sys/vm/drop_caches", "w") as drop_caches:
drop_caches.write("3")
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With