1. Edit your /etc/inittab file and add this line:
   • S0:12345:respawn:/sbin/agetty -L 9600 ttyS0 vt102
2. Execute the following command:
   • telinit q && telinit u
3. Your primary console (ttyS0) should magically appear on the serial console!

So what just happened? The /etc/inittab file is read by the init system at boot. If you added the line from step 1 and simply rebooted, you would have your console show up on the serial port right away. We told init to re-read the /etc/inittab file (telinit q) and then to re-execute itself (telinit u) while preserving the init state. Since the only change was the location of ttyS0, the console was redirected, but the system continued to run as though nothing else changed.

The reason we used the && method was because we may loose our console before we get a chance to execute telinit u. This way both commands are run and init is always executed after re-reading its config.

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import os, sys

if os.isatty(file.fileno(sys.stdin)):
    print "Reading list from STDIN."
    print "Enter your list. Press ^D to continue, ^C to quit."
    my_list = sys.stdin.readlines()
else:
    print "Thank you for passing me a list through a pipe."
    my_list = sys.stdin.readlines()

Now lets try it two ways:

First, pass it some stuff:
echo mother sister father brother | ./myapp.py

Then try it plain:
./myapp.py

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$ git config --global http.proxy http://proxy.example.com:8080
$ git config --get http.proxy

http://proxy.example.com:8080

Test it:

# cat /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts
1
#

Set it to 0 for ping replies:

# echo "0" > /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts
# cat /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts
0
#

1. mkdir /custom/perl/
2. cd /custom/perl/
3. curl -O http://www.cpan.org/src/perl-5.12.3.tar.gz
4. mkdir perl-5_12_3
5. gunzip perl-5.12.3.tar.gz
6. tar -xf perl-5.12.3.tar
7. cd perl-5.12.3
8. ./Configure -d -Dprefix=/custom/perl/perl-5_12_3
9. make
10. make test
11. make install
12. /custom/perl/perl-5_12_3/bin/perl -v
13. /custom/perl/perl-5_12_3/bin/perl -e ‘print “hello world.\n”;’
14. /custom/perl/perl-5_12_3/bin/perl -MCPAN -e shell
    • Auto configure as much as possible. Step 15 will edit it.
15. Edit /custom/perl/perl-5_12_3/lib/5.12.3/CPAN/Config.pm
    • Change the following paths:
    • ‘cpan_home’ => q[/custom/perl/perl-5_12_3/cpan/],
    • ‘build_dir’ => q[/custom/perl/perl-5_12_3/cpan/build],
    • ‘histfile’ => q[/custom/perl/perl-5_12_3/cpan/histfile],
    • ‘keep_source_where’ => q[/custom/perl/perl-5_12_3/cpan/sources],
    • ”prefs_dir’ => q[/custom/perl/perl-5_12_3/cpan/prefs],
    • ”urllist’ => [q[ftp://my.cpan.mirror/pub/cpan/]],
16. Run CPAN and install Bundle::CPAN Bundle::LWP and any required packages
17. tar -cvf /custom/perl/custom-perl5.12.13.tar /custom/perl/perl-5_12_3/*
18. gzip /custom/perl/custom-perl5.12.13.tar
19. Ship custom-perl5.12.13.tar.gz out to your matching architectures or mount it on a shared NAS.
20. Call it with #!/custom/perl/perl-5_12_3/bin/perl

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What we’re doing in a nutshell is telling PERL to push values on to the @INC array before loading any modules. You can do this on the command line, in your PERL code or with the environment variable PERL5LIB.

PERL5LIB can contain more than one value. Just set it in you .bashrc file or wherever you see fit. This method works in bash:

export PERL5LIB=/first/path/to/libs"${PERL5LIB:+:$PERL5LIB}"
export PERL5LIB=/second/path/to/libs"${PERL5LIB:+:$PERL5LIB}"
export PERL5LIB=/third/path/to/libs"${PERL5LIB:+:$PERL5LIB}"

You can check what PERL is going to use by printing out the contents of @INC. You can print an array without a loop using join() as I blogged about before:

perl -e 'print join "\n", @INC;'

Let’s put it together:
~$ perl -e 'print join "\n", @INC;'
/etc/perl
/usr/local/lib/perl/5.10.0
/usr/local/share/perl/5.10.0
/usr/lib/perl5
/usr/share/perl5
/usr/lib/perl/5.10
/usr/share/perl/5.10
/usr/local/lib/site_perl
.

~$ env|grep -i perl
~$

~$ export PERL5LIB=/first/path/to/libs"${PERL5LIB:+:$PERL5LIB}"
~$ export PERL5LIB=/second/path/to/libs"${PERL5LIB:+:$PERL5LIB}"
~$ export PERL5LIB=/third/path/to/libs"${PERL5LIB:+:$PERL5LIB}"

~$ env|grep -i perl
PERL5LIB=/third/path/to/libs:/second/path/to/libs:/first/path/to/libs

~$ perl -e 'print join "\n", @INC;'
/third/path/to/libs
/second/path/to/libs
/first/path/to/libs
/etc/perl
/usr/local/lib/perl/5.10.0
/usr/local/share/perl/5.10.0
/usr/lib/perl5
/usr/share/perl5
/usr/lib/perl/5.10
/usr/share/perl/5.10
/usr/local/lib/site_perl
.

And there it is. Your PERL apps will look in those locations starting from the top.

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if((getpwuid($<) eq "root") || ($< == 0)){
print STDOUT "Cannot run as root!\n";
exit(1);
}

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This post came about because I got a lot of hits from people looking for this information on the How To Calculate Server Heat post.

1 Watt will produce 3.412 BTU per hour

To calculate the BTU/heat output of an electrical system, substitute BTUs for Watts and use the following equation:

BTU/h = (V * I) * 3.412

Where:
V = Volts
I = Amperes (Amps or Current)

Using the simple math above, we can calculate the heat produced by an appliance on a 120v (US Standard) system drawing 2 Amps for 60 minutes (1 hour).

BTU/h = 3.412 * (120 * 2) = 818.88BTU

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Lists are one-dimensional arrays and dicts are associative arrays or hash arrays.  This means we can do the same thing we do in other languages, with syntax to match Python’s object-oriented data structures.

import pprint

# Define the list
somelist = []

# Do add some elements to the list
somelist.append({'key1':'value1', 'key2': 'value2'})
somelist.append({'key1':'value1', 'key2': 'value2'})
somelist.append({'key1':'value1', 'key2': 'value2'})

# Print it out
pp = pprint.PrettyPrinter(indent=4)
pp.pprint(somelist)

Will give you:

[   {   'key1': 'value1', 'key2': 'value2'},
{   'key1': 'value1', 'key2': 'value2'},
{   'key1': 'value1', 'key2': 'value2'}]

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