Snippets

On this page you will find script and config snippets that didn't fit in other articles. Some snippets have nature of tweaks or one-line HOWTOs, while others are just fun to run.

There is bunch of reasons why you would like to stress your CPU, one of the less serious is to play with heartbeat trigger.

cat /dev/urandom | gzip > /dev/null

Note: This will compress infinite stream of random bits and discard them. The compress level can't be changed, so you may want to run more than one instance of the script to get your average CPU load high.

Traditionally you would use top or ps command to get parameters of running processes. However if the command line is too long busybox's version of those commands will truncate it to fit your terminal window.

ps w

or

cat /proc/<PID>/cmdline

Note: Substitute <PID> with the process identifier of your process.

Edit PS1 variable in /etc/profile file:

export PS1='\[\e[1;31m\]\u@\h:\w\$ \[\e[0m\]'

This gives you normal text and background color, but red prompt, which reminds you that you are root. Other users (if exist) could get green prompt. Color codes.

It may be useful to display name of screen session if you are in one. Tip: mix some colors in. In the example the screen session has name pts-0:

root@tsunami/pts-0:~# 

local SCREEN_SESSION_NAME=$(screen -ls | sed -n 's|[^a-z]*[0-9][0-9]*\.\([a-zA-Z][a-zA-Z0-9-]*\).*Attached.*|/\1|p')
export PS1="\u@\h${SCREEN_SESSION_NAME}:\w\\$ "

Changes background color of prompt to red, when last command failed, i.e. its exit code is not equal to zero.

export PS1="\$([ \$? -ne 0 ] && echo \\\[\\\e[41m\\\])\u@\h:\w\\$\[\e[0m\] "

cat /etc/config/some.conf | nc paste.dyndns.org 1234

devstatus br-lan

cat /sbin/devstatus
#!/bin/sh
. /usr/share/libubox/jshn.sh
DEVICE="$1"
 
[ -n "$DEVICE" ] || {
	echo "Usage: $0 <device>"
	exit 1
}
 
json_init
json_add_string name "$DEVICE"
ubus call network.device status "$(json_dump)"

Here you may see that it uses jshn library

[ -s /var/state/wireless ] && wifi down || wifi up

• build your own image and set CONFIG_ATH_USER_REGD flag.
• see the whole regulatory database to find out what regulations apply.

If you use trunk version it may be useful to make local copy of packages, because new trunk version may prevent you to install kernel-related packages from official sources.

wget -r -np http://downloads.openwrt.org/snapshots/trunk/ar71xx/packages/

Assuming your architecture is ar71xx. This may require around 300 MB of free disk space.

ECC is especially favourable on low performance system like mobile phones or routers. For example, 15360 bit RSA key took 9.1 seconds to login and equally strong (actually little bit stronger) 521 bit ECDSA key took only 1.7 seconds to login. However the difference won't be really noticeble with shorter keys. To get it working, you need to:

1. compile libopenssl without NO-EC option
2. compile openssh-server and openssh-keygen with the new libopenssl in build_dir

3. ssh-keygen -t ecdsa -b 521

If you save the list of installed packages before a firmware upgrade, you can reinstall all packages that are not part of the firwmare with the script suggested in this thread.

Firstly, you will need hdparm program. Then locate your attached drive in /dev directory - typically /dev/sda1 or /dev/sda2 etc.

opkg update && opkg install hdparm
hdparm -t /dev/sda1

See also USB Benchmarks and Filesystems performance page.

Flashes on activity in Hurricane Electric 6in4 tunnel. Taken from /etc/config/system file:

Note:detailed configuration is here.

All edits take place in /etc/profile file. We place the scripts in this section below the cat /etc/banner.

For those who uses the screen command. This will print for example this:

And the script for it:

local screenlabel=$(screen -ls | sed -n 's|^\([0-9][0-9]*\) Socket.*| \1 Screen sessions: |p')
screen -ls | sed -n 's|[^a-z]*[0-9][0-9]*\.\([a-zA-Z][a-zA-Z0-9-]*\).*|\1|p' | sed -e "s|^|${screenlabel}|" -e :a -e N -e 's|\n|, |' -e ta

Note: screenlabel variable just contain number of sessoins and static text, so if you are ok with just list of screen sessions you can skip it and make it little bit more clear. Second line first get names of sessions, then add screenlabel variable in front of it and then put it all in one line.

Less useful script, but anyway ;)

echo " Entropy:" $(cat /proc/sys/kernel/random/entropy_avail)/$(cat /proc/sys/kernel/random/poolsize)