UNIX Management ¶

Author:: Dimitry Dukhovny

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Networking ¶

Get IP address ¶

1ifconfig -a

For a particular interface, such as eth0, use

1ifconfig eth0

Alternately…

1ip a

Set the new IP address ¶

For these examples, we will assign 192.168.100.100 in our /24 to the interface eth0 with a default gateway of 192.168.100.254.

Set the IP directly from the commandline ¶

ifconfig eth0 192.168.100.100 netmask 255.255.255.0
route add default gw 192.168.100.254

Set the IP in configuration files on a Redhat-like systems ¶

/etc/network/interfaces/ifcfg-eth0¶

TYPE=Ethernet
BOOTPROTO=none
DEFROUTE=yes
IPV4_FAILURE_FATAL=no
IPV6INIT=no
IPV6_FAILURE_FATAL=no
NAME=eth0
DEVICE=eth0
ONBOOT=yes
IPADDR=192.168.100.100
NETMASK=255.255.255.0 # for Centos6
PREFIX=24 # for Centos7
GATEWAY=192.168.100.254
DNS1=192.168.100.1
DNS2=192.168.100.2
DOMAIN=mydomain.gov

Set the IP in configuration files on a Debian-like systems ¶

/etc/network/interfaces¶

source /etc/network/interfaces.d/*

# The loopback network interface
auto lo
iface lo inet loopback
        address 127.0.0.1

# The primary network interface
iface eth0 inet static
        address 192.168.100.100
        netmask 255.255.255.0
        gateway 192.168.100.254
        dns-nameservers 192.168.100.1

Patches and Updates ¶

Update package list in Redhat-like systems ¶

yum check-update
yum update

Update package list in Debian-like systems ¶

apt-get update
apt-get upgrade

Trouble: Stale process or process with runaway threads ¶

Use this to kill processes of a certain name owned by a certain user that is older than a certain time.

In this example, we want to kill every httpd process owned by apache that is older than five hours.

/usr/bin/find /proc -maxdepth 1 -user apache \
 -type d -mmin +300 -exec basename {} \; | \
 xargs ps | grep httpd | awk '{print $1}' | \
 xargs -i kill -HUP {}

Trouble: My process claims a file is not found ¶

strace your way through the stack to see where it looks for files
Assuming a program called black_box in the current directory…

strace -f -s 255 -o /tmp/black_box.out ./black_box

Trouble: My process claims it is missing a library ¶

List the expected libraries and install any missing ones.
- error while loading shared libraries
- cannot open shared object file
Assuming a program called black_box in the current directory…

ldd ./black_box 2>&1 | grep "not found"