Code Shop

I needed to limit access to Redis running on port 6379 to localhost on a Linux server. Here is the code to run that. It basically disallows anyone one who is not 127.0.0.1 from access to the server.

 
sudo iptables -A INPUT -i eth0 ! -s 127.0.0.1 -p tcp --destination-port 6379 -j DROP 

This could be generalized to other services i.e MySQL, PostgresSQL, etc. but here it is.

I always forget the different date specifiers for the
date command so here they are in all their glory.

%%	a literal %
%a	locale’s abbreviated weekday name (e.g., Sun)
%A	locale’s full weekday name (e.g., Sunday)
%b	locale’s abbreviated month name (e.g., Jan)
%B	locale’s full month name (e.g., January)
%c	locale’s date and time (e.g., Thu Mar 3 23:05:25 2005)
%C	century; like %Y, except omit last two digits (e.g., 21)
%d	day of month (e.g, 01)
%D	date; same as %m/%d/%y
%e	day of month, space padded; same as %_d
%F	full date; same as %Y-%m-%d
%g	last two digits of year of ISO week number (see %G)
%G	year of ISO week number (see %V); normally useful only with %V
%h	same as %b
%H	hour (00..23)
%I	hour (01..12)
%j	day of year (001..366)
%k	hour ( 0..23)
%l	hour ( 1..12)
%m	month (01..12)
%M	minute (00..59)
%n	a newline
%N	nanoseconds (000000000..999999999)
%p	locale’s equivalent of either AM or PM; blank if not known
%P	like %p, but lower case
%r	locale’s 12-hour clock time (e.g., 11:11:04 PM)
%R	24-hour hour and minute; same as %H:%M
%s	seconds since 1970-01-01 00:00:00 UTC
%S	second (00..60)
%t	a tab
%T	time; same as %H:%M:%S
%u	day of week (1..7); 1 is Monday
%U	week number of year, with Sunday as first day of week (00..53)
%V	ISO week number, with Monday as first day of week (01..53)
%w	day of week (0..6); 0 is Sunday
%W	week number of year, with Monday as first day of week (00..53)
%x	locale’s date representation (e.g., 12/31/99)
%X	locale’s time representation (e.g., 23:13:48)
%y	last two digits of year (00..99)
%Y	year
%z	+hhmm numeric timezone (e.g., -0400)
%Z	alphabetic time zone abbreviation (e.g., EDT)

If you want to point your home computer to a domain or subdomain you own, instead of using something like DynDNS, you can use Linode. If you have Linode hosting your DNS the Linode API makes it a relative breeze to update. Here is the code:

I really like Dropbox. It's a convienient way to sync all your
computers without using rsync and what not. However, the thing that
bugs me the most is keeping my dotfiles in sync as I usualyl forget to
sync between computers when I change them. Thanksfully, Dropbox makes
this easier.

1. Create a directory in your Dropbox folder.
2. Move your dotfiles from $HOME to that folder. Change the prefix . with _.
3. Add this file (I named it dotfiler.sh, but you can name it whatever you want)

 
#!/bin/sh 
 
for file in _* 
do 
 ln -s -n -f `pwd`/$file $HOME/${file/#_/.} 
done 

4. chmod +x the new file. (Currently, executable flag doesn't move
from one machine to another. So probably have to do this on each
machine.)
5. Run the file in your not dotfiles directory.

This should keep all your dotfiles in sync whatever computer you are
using. If you also added .profile and .bashrc make sure that you take
your platform into account i.e., Linux, Mac OS X.

Run the script whenever you add a new dotfile.

Unix is a multitasking operating system (like most everyday operating systems nowadays) and as such it has and idea on how to do handle jobs. Jobs are executing which happen on a per shell basis as opposed to processes. Here is a summary of everything that you need to know about UNIX jobs. 

I setup NFS4 on my home server to host my mp3s for iTunes to access.
However, I had trouble getting the Mac GUI to mount the NFS drives. So
I instead decided to use the command line.

 
sudo /sbin/mount_nfs -o resvport krusty:/home/abhi/iTunes MusicMount/ 

This should mount a nfs mount. Just set that MusicMount to be where
you want iTunes to store your files. So far this has been working out
great.

I found this xterm schema to be quite nice. Put in ~/.Xdefaults file.

 

 
XTerm*background: #000000 
XTerm*foreground: #9f9f9f 
XTerm*color0: #000000 
XTerm*color1: #9e1828 
XTerm*color2: #aece92 
XTerm*color3: #968a38 
XTerm*color4: #414171 
XTerm*color5: #963c59 
XTerm*color6: #418179 
XTerm*color7: #bebebe 
XTerm*color8: #666666 
XTerm*color9: #cf6171 
XTerm*color10: #c5f779 
XTerm*color11: #fff796 
XTerm*color12: #4186be 
XTerm*color13: #cf9ebe 
XTerm*color14: #71bebe 
XTerm*color15: #ffffff 

Lately, I've been trying to compile Chromium on my desktop and I had been constantly getting an error associated with linking:

collect2: ld terminated with signal 9 [Killed]

After Googling around apparently the problem had to do with running out of swap space which causes the linking to fail. Chromium needs almost 700mb more memory to link than I was providing so it was failing. Interestingly, Linux has a really clean solution to increase the swap space.

sudo dd if=/dev/zero of=/swapfile bs=1024 count=1048576
sudo mkswap /swapfile
sudo swapon /swapfile

These three commands will create an empty file of 1gb, make that a swap file, and turn it on to be used.

 

I'm getting a bit tired of using Firefox on Linux. It tends to be slow and bloated and though I would like to use Chrome it is not compiling on my Arch system. I think it has something to do with a lack of memory to link the various object files (I only have 512mb of ram on my desktop). So I'm using this lightweight WebKit based browser called Arora which is pretty fast. I mean the pages render ridiculously fast compared to Firefox. I recommend it to anyone on Linux, that is until Chrome comes out for Linux.