RHEL/CentOS quick reference

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Services

Note: For RHEL 7+ see Systemd

To stop/start/restart services:

sudo /sbin/service [service name] stop/start/restart

Ex:

sudo /sbin/service networking restart

To change startup services:

sudo /sbin/chkconfig --list

(lists startup services and runlevels)

sudo /sbin/chkconfig [service] [on/off/reset] [--level <runlevels>]

Ex:

sudo /sbin/chkconfig bluetooth off

(disables bluetooth service at all runlevels)

sudo /sbin/chkconfig cups off --level 5

(disables cups at runlevel 5)

sudo /sbin/chkconfig cups reset

(resets cups service to default runlevels (2,3,4,5))

sudo /sbin/chkconfig cups on –level 1234

(turns cups service on on runlevels 1,2,3,4)

Networking

To change the hostname/IP address (RHEL 6 and below)

Edit /etc/hosts

127.0.0.1        localhost.localdomain localhost
192.168.0.100    myhost.example.com myhost
::1              localhost6.localdomain6 localhost6

If this machine is using DHCP, instead of the IP address for the second line, you can use something like 127.0.1.1

Edit /etc/sysconfig/network

NETWORKING=yes
NETWORKING_IPV6=no
HOSTNAME=myhost.example.com
GATEWAY=192.168.0.1

Edit /etc/sysconfig/network-scripts/ifcfg-eth0 (or eth1 for eth1, etc.)

DEVICE=eth0
ONBOOT=yes
BOOTPROTO=static
HWADDR=00:01:02:03:04:05
IPADDR=192.168.0.100
NETMASK=255.255.255.0
NETWORK=192.168.0.0
BROADCAST=192.168.0.255

If this machine is using DHCP, leave the IPADDR line out, and the BOOTPROTO line should be:
```
BOOTPROTO=dhcp
```
Also, add this line:
```
DHCP_HOSTNAME=myhost.example.com
```
Optionally, add these lines:
```
PEERDNS=no
PEERNTP=no
```

Recreate NIC on a VM without incrementing device value (e.g. eth1, eth2)

Back up and remove /etc/udev/rules.d/70-persistent-net.rules, then reboot

RHN (RHEL only)

If the system doesn’t appear to be registered with RHN:

/usr/sbin/rhnreg_ks --force --profilename `hostname -f` --activationkey=ACTIVATION_KEY

If this doesn’t work, /etc/sysconfig/rhn/up2date may have been changed from the original. To fix this:

Make sure the serverURL is set to https://xmlrpc.rhn.redhat.com/XMLRPC
```
serverURL=https://xmlrpc.rhn.redhat.com/XMLRPC
```
If that doesn’t work:
1. Get the version of rhn-client-tools on the machine:
```
rpm -qa rhn-client-tools
```
2. On a machine that is registered with RHN, download that version of rhn-client-tools:
```
yumdownloader rhn-client-tools-X.X.X
```
3. Copy it to the original machine, and install it:
```
scp rhn-client-tools-X.X.X mymachine:~
rpm -iv --force rhn-client-tools-X.X.X
```

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