daily debugging tips and toolbox

* debugging tips
strace::
http://www.thegeekstuff.com/2011/11/strace-examples/

where is the log files of specified process (e.g. nginx)?
@firstly, find your process's pid
ubuntu@ip:~ $ ps -ef | grep nginx
root     13622     1  0 Mar03 ?        00:00:00 nginx: master process /usr/sbin/nginx
www-data 13623 13622  0 Mar03 ?        00:03:19 nginx: worker process
www-data 13624 13622  0 Mar03 ?        00:00:00 nginx: worker process
www-data 13625 13622  0 Mar03 ?        00:03:19 nginx: worker process
www-data 13626 13622  0 Mar03 ?        00:03:19 nginx: worker process
ubuntu   19058 18961  0 10:31 pts/0    00:00:00 grep --color=auto nginx
@secondly, using lsof to find all handle of that "pid", then grep it
ubuntu@ip:~ $ sudo lsof -f -p 13622 | grep log
nginx   13622 root    2w   REG              202,1        0 145222 /var/log/nginx/error.log
nginx   13622 root    5w   REG              202,1        0 135398 /var/log/nginx/access.log
nginx   13622 root    6w   REG              202,1        0 145222 /var/log/nginx/error.log

which process is listen on port 80?
ubuntu@ip:~ $ sudo lsof -i:80
COMMAND   PID     USER   FD   TYPE DEVICE SIZE/OFF NODE NAME
nginx   13622     root    7u  IPv4  27232      0t0  TCP *:http (LISTEN)
nginx   13623 www-data    7u  IPv4  27232      0t0  TCP *:http (LISTEN)
nginx   13624 www-data    7u  IPv4  27232      0t0  TCP *:http (LISTEN)
nginx   13625 www-data    7u  IPv4  27232      0t0  TCP *:http (LISTEN)
nginx   13626 www-data    7u  IPv4  27232      0t0  TCP *:http (LISTEN)

what's my process's environemnt variables?
[vagrant@vagrant-centos-6-64 ~] $ ps -ef | grep apache
apache    2136  1382  0 10:11 ?        00:00:00 /usr/sbin/httpd
[vagrant@vagrant-centos-6-64 ~] $ sudo cat /proc/1382/environ
TERM=linuxPATH=/sbin:/usr/sbin:/bin:/usr/binrunlevel=3RUNLEVEL=3LANGSH_SOURCED=1PWD=/LANG=Cprevious=NPREVLEVEL=NCONSOLETYPE=vtSHLVL=3UPSTART_INSTANCE=UPSTART_EVENTS=runlevelUPSTART_JOB=rc_=/usr/sbin/httpd

let mysql log the queries?
@execute following command in mysql console
SET GLOBAL log_output = 'FILE'; Set GLOBAL general_log_file = '/tmp/mysql.log'; SET GLOBAL general_log = 'ON';
@ or directly in bash
 $ mysql -uroot -pYOUR-PASSWORD -e "SET GLOBAL log_output = 'FILE'; Set GLOBAL general_log_file = '/tmp/mysql.log'; SET GLOBAL general_log = 'ON';"
@ then tail /tmp/mysql.log, see the quries against mysql
 $ tail -f /tmp/mysql.log

how to monitor http request/response of this machine?
@install justniffer on mac
 $ brew install boost
 $ brew install justniffer
@ Capture all tcp traffic
 $ sudo justniffer -i eth0 -r
        GET /null_main.c HTTP/1.1
        Host: localhost:9000
        Connection: keep-alive
        Cache-Control: max-age=0
        Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
        User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_7_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/27.0.1453.110 Safari/537.36
        Accept-Encoding: gzip,deflate,sdch
        Accept-Language: en-US,en;q=0.8
        If-Modified-Since: Sat, 20 Oct 2012 09:17:23 GMT
        
        HTTP/1.0 200 OK
        Server: SimpleHTTP/0.6 Python/2.7.1
        Date: Thu, 06 Jun 2013 13:27:41 GMT
        Content-type: text/plain
        Content-Length: 46
        Last-Modified: Sat, 20 Oct 2012 09:17:23 GMT
        
        /* null_main.c */
        
        int main() {
          return 0;
        }
@ Capture only http traffic
 $ sudo justniffer -i eth0 -r -p "port 80 or port 8080"
 
@Capture smtp traffic (usually using tcp port 25)
 $ sudo justniffer -i eth0 -r -p "port 25"
        220 plecno.com ESMTP Postfix (Ubuntu)
        
        EHLO unknown.localnet
        250-plecno.com       
        250-PIPELINING       
        250-SIZE             
        250-VRFY             
        250-ETRN             
        250-STARTTLS         
        250-ENHANCEDSTATUSCODES
        250-8BITMIME           
        250 DSN
        ...
        --Boundary-00=_ZI47J3FTNXn+25g
        Content-Type: text/html;
        charset="us-ascii"
        Content-Transfer-Encoding: 7bit
        
        <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0//EN"
        "http://www.w3.org/TR/REC-html40/strict.dtd">
        <html>
        <head>
        ...

How to monitor changes in directory?
@run following command, and try to touch/rm files. the results of `watch` will changing.
 $ watch -d -n 0.1 "ls"


How to start a HTTP server on port 3000 for files in directory ~?
 $ cd ~
 $ python -m SimpleHTTPServer 3000

        

TO BE CONTINUE::::