Check how long a MongoDB instance was running
Answer:
To see how long a MongoDB instance was running, you can login into the mongo shell, and enter
db.serverStatus().uptime / 3600
The above command reply the value in term of hours.
Apr 152013
Linux Ask!
Apr 112013
How to get the startup warning from MongoDB?
Answer:
The easiest way is login into the MongoDB using the shell, enter the command:
db.adminCommand({getLog: "startupWarnings" })
Apr 042013
Constant in Ruby
Answer:
In Ruby, a class constant has a name starting with an uppercase character, e.g.
Foo = 'bar'
puts FooWhere you try to re-define the constant, a warning message will be shown, e.g.
Foo = 'bar'
Foo = '123'
(irb):18: warning: already initialized constant FooMar 292013
Global and Local variable in Ruby
Answer:
In Ruby, global variable has a name beginning with $, e.g.
$foo = 'bar'
puts $fooIn contrast, local variable has a name start with a lower case letter or an underscore character, e.g.
foo = 'bar'
puts fooMar 092013
Traceroute using TCP
Answer:
It is common now for a server to disable the ICMP and make commands like *ping* & *traceroute* failed to do the diagnostics. However, newer version of *traceroute* have a TCP mode that if you know a particular server is opening a port for TCP connection, then you can use command like..
# sudo traceroute -T www.google.com
traceroute to www.google.com (74.125.235.242), 30 hops max, 60 byte packets
1 136.182.34.2 (136.182.34.2) 0.557 ms 0.572 ms 0.621 ms
2 125.235.129.111 (125.235.129.111) 11.232 ms 11.242 ms 11.235 ms
3 otejbb205.int-gw.kddi.ne.jp (124.215.194.161) 1.602 ms otejbb206.int-gw.kddi.ne.jp (124.215.194.177) 2.123 ms 2.119 ms
4 ix-ote210.int-gw.kddi.ne.jp (106.187.6.114) 11.182 ms ix-ote210.int-gw.kddi.ne.jp (106.187.6.98) 11.156 ms ix-ote210.int-gw.kddi.ne.jp (106.187.6.114) 11.199 ms
5 203.181.102.94 (203.181.102.94) 63.248 ms 63.272 ms 63.262 ms
6 209.85.249.195 (209.85.249.195) 2.523 ms 2.252 ms 2.191 ms
7 64.233.175.0 (64.233.175.0) 6.512 ms 6.448 ms 6.537 ms
8 64.233.174.0 (64.233.174.0) 11.154 ms 11.474 ms 10.738 ms
9 216.239.43.243 (216.239.43.243) 11.108 ms 11.713 ms 12.141 ms
10 kix01s02-in-f18.1e100.net (74.125.235.242) 11.103 ms 10.582 ms 10.882 ms