'RTNETLINK answers: File exists'

Question

When I added the delay command, paramiko returns back "2" as exit status(while it returns "0" for bandwidth command setting). Is 2 alright? (Googling didn't help with this, I am guessing 2 must be an error of some sort).

The command I use is:-

delay_cmd = "sudo tc qdisc add dev eth0 parent 1: handle 1: netem delay %dms" %(delay)

We were basically trying to follow this:

# tc qdisc add dev eth0 root netem delay 100ms

from an online tutorial.

The block of commands which should set the bw,filter and delay is this. (I am guessing I might be messing up with the parent/class ids). Can you see what I might be doing wrong?

   cmd2 = "sudo tc class add dev %s parent 1: classid 1:1 htb rate %dmbps ceil %dmbps" % (interface, bandwidth, 2*bandwidth )
    filter_cmd = "sudo tc filter add dev %s protocol ip parent 1:0 prio 1 u32 match ip dst %s/%d flowid 1:1" % (interface, ip, subnetmasklength)
    delay_cmd = "sudo tc qdisc add dev eth0 parent 1:0 handle 1: netem delay %dms" %(delay)

This is the error I receive:

'RTNETLINK answers: File exists'

This is our script for setting the delay and bandwidth:

def exec_bw_config2(ssh, interface, bandwidth, ip, subnetmasklength, delay):
    clear_bw_config2(ssh, interface)
    # create a qdisc (queuing discipline), 12 is default class
    cmd1 = "sudo tc qdisc add dev %s root handle 1: htb default 12" % interface
    print cmd1
    block_exec(ssh, cmd1)

    # define the performance for default class
    cmd2 = "sudo tc class add dev %s parent 1: classid 1:1 htb rate %dmbps ceil %dmbps" % (interface, bandwidth, 2*bandwidth )
    print cmd2

    block_exec(ssh, cmd2)


    filter_cmd = "sudo tc filter add dev %s protocol ip parent 1:0 prio 1 u32 match ip dst %s/%d flowid 1:1" % (interface, ip, subnetmasklength)
    print filter_cmd
    block_exec(ssh, filter_cmd)


delay_cmd = "sudo tc qdisc add dev eth0 parent 1: handle 1: netem delay %dms" %(delay)
    print delay_cmd
    block_exec(ssh, delay_cmd)

So is anything wrong with delay_cmd above?

This is how we call it in our code:

def main():
    myhosts = ["10.0.1.192", "10.0.1.191", "10.0.1.190"]
    username="ubuntu"
    port=22
    #key = get_private_key()
    for host in myhosts:
        ssh = get_ssh(username, host, port)
        clear_bw_config2(ssh, "eth0")
        exec_bw_config2(ssh, "eth0", int(sys.argv[1]) , "10.0.1.0", 24, int(sys.argv[2]))

    # iterate over hosts here
    # for everyhost,
    # 1. create ssh connection
    # 2. run the exec_bw_config with params
    return

On a further note what's the difference between parent 1: handle and parent 1:2 handle per se?

score 1 · Answer 1 · answered Dec 18 '15 at 10:51

It's not a fatal error: 'File exists' is just saying that such emulation is already defined and 'Invalid argument' that such emulation is not known to kernel or already deleted.

Quick small sample:

# ~ $ sudo tc qdisc add dev eth0 root netem delay 0ms
# ~ $ sudo tc qdisc add dev eth0 root netem delay 0ms
RTNETLINK answers: File exists
# ~ $ sudo tc qdisc del dev eth0 root netem delay 0ms
# ~ $ sudo tc qdisc del dev eth0 root netem delay 0ms
RTNETLINK answers: Invalid argument

score 1 · Answer 2 · edited Dec 28 '18 at 16:20

1

use:

sudo tc qdisc replace dev eth0 root netem delay 100ms

or:

sudo tc qdisc del dev eth0 root
sudo tc qdisc add dev eth0 root netem delay 100ms

edited Dec 28 '18 at 16:20

AS Mackay

2,831
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answered Dec 28 '18 at 15:46

kaustubh mehta

11
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'RTNETLINK answers: File exists'

2 Answers2