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Disabling RHEL 6 Network Manager

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RHEL 6  configured to use NetworkManager, even if we install server. NetworkManager is a desktop component, which is semi-useless for rack mounted servers with static IP and cable connection (it can be useful for initial installation, when your switch is not yet configured; you can use instead wireless card  to configure server via wireless network or USB to Ethernet adapter which you can connect to desktop DHCP segment). 

Moreover Network Manager is essentially a DHCP beast and it overwrites /etc/resolv.conf if you configure static IP parameters (see Network Manager overwrites resolv.conf for details) on reboot.  That comes to very unpleasant surprise as servers are not rebooted often and at this point you do not expect this Trojan horse inside your environment ;-)

Functionally Network Manager replaces old /etc/init.d/network script, but its useful functionality is limited mainly to wireless networks and desktops/laptops which use DHCP. It typically causes allergy for sysadmins who get used to static IP stack assignments.  And overwriting /etc/resolv.conf is just one of several side effects.

How to Disable Network Manager completely

To disable Network Manager please follow instructions below.  First you need to disable it from init and shutdown the service:

chkconfig NetworkManager off
service NetworkManager stop

How to disable Network Manager for particular interfaces only

If you need wireless connection on your server, or connection that you need to control similarly, you might try to excluded some Ethernet interfaces from control of network manager. In this case you need

In the  /etc/sysconfig/network-scripts/ifcfg-eth0 only one parameter matter: to disable NM you can put NM_CONTROLLED="no" 

DEVICE="eth0"
NM_CONTROLLED="no"
ONBOOT="yes"
HWADDR=00:50:56:AB:50:90
TYPE=Ethernet
BOOTPROTO=none
IPADDR=10.12.36.89
PREFIX=22
GATEWAY=10.12.36.1
DNS1=10.12.5.20
DOMAIN="some.company.net"
DEFROUTE=yes
IPV4_FAILURE_FATAL=yes
IPV6INIT=no
NAME="System eth0"

After restarting NeworkManager service verify that Network Manager is successfully disabled for eth1. 

nmcli dev status
Commnad nmcli is in /usr/bin. Here is synopsys 
nmcli
Usage: nmcli [OPTIONS] OBJECT { COMMAND | help }

OPTIONS
  -t[erse]                                   terse output
  -p[retty]                                  pretty output
  -m[ode] tabular|multiline                  output mode
  -f[ields] |all|common   specify fields to output
  -e[scape] yes|no                           escape columns separators in values
  -v[ersion]                                 show program version
  -h[elp]                                    print this help

OBJECT
  nm          NetworkManager status
  con         NetworkManager connections
  dev         devices managed by NetworkManager

Enable network service so that particular interface (eth0 in our example) is activated by network service automatically upon boot.

Now it make sense that you can specify DNS server /etc/sysconfig/network-scripts/ifcfg-eth0  per interface.

Removing Network Manager completely from the OS

You can also remove NetworkManager completely. For example

rpm -qa | fgrep "Network"

And based on result of the search delete RPMs involved. 

rpm -e NetworkManager-0.8.1-66.el6.x86_64 NetworkManager-gnome-0.8.1-66.el6.x86_64
Note:

If you specified network parameters during install the  GATEWAY  info is duplicated in the /etc/sysconfig/network: 

NETWORKING=yes
HOSTNAME=box89.some.company.net
GATEWAY=10.12.36.1

If you change gateway manually without using GUI applet you need to change it in all places.

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Please visit nixCraft site. It has material well worth your visit.

Dr. Nikolai Bezroukov

Introducing NetworkManager by Rosanna Yuen January 2005

How to disable Network Manager on Linux - Linux FAQ

nmcli(1) tool for controlling NetworkManager - Linux man page

networkmanager.conf(5) - Linux man page

[ifupdown]

This section contains ifupdown-specific options and thus only has effect when using ifupdown plugin.
managed=false | true
Controls whether interfaces listed in the 'interfaces' file are managed by NetworkManager. If set to true, then interfaces listed in /etc/network/interfaces are managed by NetworkManager. If set to false, then any interface listed in /etc/network/interfaces will be ignored by NetworkManager. Remember that NetworkManager controls the default route, so because the interface is ignored, NetworkManager may assign the default route to some other interface. When the option is missing, false value is taken as default.

nm-system-settings.conf(5) - Linux man page

nm-tool(1) - Linux man page

Ubuntu Manpage nmcli - command-line tool for controlling NetworkManager

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Last modified: June, 04, 2016