Using netcat

Send a string (e.g. to a Graphite server)

echo "metrics.test.random $RANDOM $(date +%s)" | nc 10.60.35.50 2003

Test status of a TCP daemon

nc -vz someserver port

-v: verbose
-z: scan for listening daemons but send no data

Disable IPv6 on CentOS

echo 'install ipv6 /bin/true' > /etc/modprobe.d/ipv6.conf
init 6

This process disables the IPv6 kernel module entirely. It can be considered good form, but by no means necessity, to do the following:

chkconfig ip6tables off

Also in /etc/sysconfig/network-scripts/ifcfg-*:

IPV6INIT=no
IPV6_AUTOCONF=no

To verify, the following should produce empty output:

lsmod | grep v6

Set static host name (Ubuntu)

sudo hostname myhost #

echo 'myhost' | sudo tee /etc/hostname

VirtualBox video resolution: guest only allows small video resolutions

Symptom: Guest OS (Kubuntu) only allows 640x480 video resolution

Solution: Increase video memory allocation on virtual machine - on VirtualBox: Settings > Display > Video > Video Memory (set to >64MB)