What to do when lighttpd won’t start and won’t give out any error output?

So you upgraded your server, or just all of a sudden you try to start lighttpd, it says the server started ok, but you check and there’s no lighttpd process.

You then go after your error log files, and nothing… what the fuck is happening?

try this to attempt to debug.

sudo strace -ff /usr/local/sbin/lighttpd -f /etc/lighttpd/lighttpd.conf

In my case the output showed me lighttpd was having permission issues trying to access a log file…

[pid 28073] close(5) = 0
[pid 28073] munmap(0x7fe884c71000, 4096) = 0
[pid 28073] write(3, "2015-02-04 11:04:23: (log.c.164)"..., 49) = 49
[pid 28073] close(2) = 0
[pid 28073] open("/dev/null", O_RDWR) = 2
[pid 28073] brk(0x2203000) = 0x2203000
[pid 28073] open("/home/bh/access.log", O_WRONLY|O_CREAT|O_APPEND, 0644) = -1 EACCES (Permission denied)
[pid 28073] write(3, "2015-02-04 11:04:23: (log.c.118)"..., 98) = 98
[pid 28073] write(3, "2015-02-04 11:04:23: (server.c.1"..., 83) = 83

Top Eclipse (IDE) features I can’t live without

(If you are in Windows, replace “Cmd” for “Ctrl”, and “Option” for “Alt”)

Cmd + 1: Create variables out of function’s outputs, get suggestions to fix issues.

“Shift + Cmd + T”: Open Type.

“Shift + Cmd + R”: Open Resource.

Select element and press “Option + Cmd + R” to rename a class, variable, method, the refactor will be performed throughout the entire project flawlessly.

Select element and press “Cmd + T”: Show Type Hierarchy, great to know what classes implement an interface, or what classes extend an abstract class.

How to use Google’s calculator to convert Amps and Volts, to kWh

Say you have an electric engine that consumes 8 amps at 12 V, and you would like to know how much this would translate in kilowatt hours?

Go to Google’s search box and type

8 amps * 12 v * 1 hour

Screen Shot 2013-05-26 at 8.27.15 AM

And you will get the total output in Joules, which is 345,600 joules.

Then tell google

345600 joules to kwh

And google will tell you

0.096 kilowatt hours (which is what a small electric fan will consume in an hour), or the same as 8 * 12 = 96 watts * 1 hr, 96 Wh

Screen Shot 2013-05-26 at 8.29.47 AM

Quick N Dirty way to Map Commands to remote servers via ssh

You may be running several independent but similar servers at the same time and wasting time by executing commands in all of them one by one.

Wouldn’t it be nice to send a command to all of them at once? or to monitor all of them at once.

The following script can be used as a building block to more complex automation tasks for a small size set of servers. (If you’re managing over 50 servers, I’d probably consider looking a different way to arrange servers (map/reduce cluster), but if you’re doing something below that number this might suffice)

[code lang=”python”]
#!/usr/bin/python

#########################################################
# Author: Angel Leon (gubatron@gmail.com) – October 2009
#
# Invokes a command locally and invokes the same command
# in all machines under the specified username, servers
#
# Requirement: Have a public ssh_key for that user on all
# the other machines so you don’t have to authenticate
# on all the other machines.
#########################################################
import sys
import os

# set the username that has access to all the machines here
user=’safeuser’

# add all your server names here
servers=[‘server1.mydomain.com’,’server2.mydomain.com’,’server3.mydomain.com’]

if __name__ == "__main__":
if len(sys.argv) < 2:
print "Usage: ssh_map_command <cmd>"
sys.exit(0)

cmd= ‘ ‘.join(sys.argv[1:])

#Execute locally first
print cmd
os.system(cmd)

#Execute for all the servers in the list
for server in servers:
remote_cmd="ssh %s@%s %s" % (user,server,cmd)
print remote_cmd
os.system(remote_cmd)
print
[/code]

Save as ssh_map_command and chmod +x it.

Sample uses
Check the average load of all machines at once (then use output to mitigate high load issues)
[code lang=”shell”]$ ssh_map_command uptime[/code]

Send HUP signal to all your web servers (put it in an alias or other script… and that’s how you start building more complex scripts)
[code lang=”shell”]$ ssh_map_command ps aux | grep [l]ighttpd | kill -HUP `awk {‘print $2’}`[/code]

Check if processes are alive, check memory usage on processes across different machines, grep remote all logs at once, svn up on all machines, rsync from one to many, hey, you can even tail -f and grep all the logs at once, you can go nuts with this thing. Depends on what you need to do.

Requirements

Security Advisory
Make sure only the desired user has read/write/execute access to it and keep your private ssh keys safe (preferably only read and execute for the owner, and no permissions whatsoever to anybody else chmod 500 ssh_mod_map), if possible change them as often as possible, for it may become a big security whole if an attacker can manage to write code on this script, specially if you have cronjobs invoking it. Your attacker would only need to change code here to mess up all of your machines.

Disclaimer and Call for Knowledge
Please, if someone knows of a standard way to map commands to multiple servers, please let me know in the comment section, in my case I needed a solution and I wrote a quick and dirty python script and tried to secure it as best as I could, by no means I’m saying that this is the best solution to mapping commands, in fact I believe it might be the least efficient way, however it works good enough for my personal needs.

How to remove a Bra with one Hand (POV)

I learned the trick from a couple of other videos in youtube, however I thought they were badly shot and I decided to make my own version from the point of view of the person taking the bra off.

Wish I someone had taught me this trick years ago, thanks Internet for being such a great teacher.