List of Imp unix commands

I am trying to list all the important administrative commands here from system point of view :

= Show working directory of the process
pwdx PROCESS_ID

= display the current open file of process
pfiles PROCESS_ID

= Display inter process communication status
ipcs
output :

bash-3.00$ ipcs
IPC status from  as of Thu Mar  3 23:56:08 EST 2011
T         ID      KEY        MODE        OWNER    GROUP
Message Queues:
Shared Memory:
Semaphores:

= List all the processes sorted by CPU usages
top
Explanation : The command shows all the processes sorted by CPU utilization level. Also displays load average, number of processes in different states ( sleeping, zombie, stopped, running 1 ). It updates screen after fix delay ( i think its 1 second ). Also displays level of cpu and memory utilization. i.e. real, free, swap in use.

bash-3.00$ top
load averages:  0.09,  0.11,  0.13                                     23:59:57
238 processes: 231 sleeping, 6 stopped, 1 on cpu
CPU states:     % idle,     % user,     % kernel,     % iowait,     % swap
Memory: 2048M real, 922M free, 807M swap in use, 32G swap free

   PID USERNAME THR PRI NICE  SIZE   RES STATE    TIME    CPU COMMAND
  6431 www        3  39    5 8912K 4192K sleep    0:00  0.30% httpd
   511 odyssey   18  43    5    0K    0K sleep    0:35  0.26% java
  5114 k35patel   1  40    0 3144K 2496K sleep    0:00  0.21% bash
  6523 k35patel   1  40    0 1920K 1296K cpu/0    0:00  0.14% top
  5919 www        3  33    5 8920K 4280K sleep    0:00  0.07% httpd
  5871 www        3  29    5 8960K 4280K sleep    0:00  0.07% httpd
  5604 www        3  33    5 9016K 5192K sleep    0:00  0.06% httpd
 15650 ikotsire   1  48    0 3648K 3216K sleep    0:00  0.06% tcsh
  5082 k35patel   1  58    0 7944K 2696K sleep    0:00  0.06% sshd
  6348 www        3  33    5 8944K 4232K sleep    0:00  0.05% httpd
  5918 www        3  43    5 8944K 4464K sleep    0:00  0.05% httpd
  6427 www        3  29    5 8936K 4216K sleep    0:00  0.05% httpd
  5576 www        3  29    5 9040K 5384K sleep    0:00  0.04% httpd
  5917 www        3  41    5 8976K 4544K sleep    0:00  0.04% httpd
  5916 www        3  40    5 8968K 4504K sleep    0:00  0.03% httpd
  6347 www        3  33    5 8944K 4224K sleep    0:00  0.03% httpd
    68 root       7  42    0 3744K 2424K sleep  290:43  0.02% picld

Alternative of top command would be "prstat -a"

= How to check what is the page size of the memory?
pagesize

= display the network statistic using simple command.
netstat -a or netstat
So protocol, local to remote address connection is shown. State is also seen.

output would look like :
C:\Windows\system32>netstat

Active Connections

  Proto  Local Address          Foreign Address        State
  TCP    127.0.0.1:895          kush-PC:6751           ESTABLISHED
  TCP    127.0.0.1:1036         kush-PC:27015          ESTABLISHED
  TCP    127.0.0.1:4488         kush-PC:4489           ESTABLISHED
  TCP    127.0.0.1:4489         kush-PC:4488           ESTABLISHED
  TCP    127.0.0.1:4721         kush-PC:4722           ESTABLISHED
  TCP    127.0.0.1:4722         kush-PC:4721           ESTABLISHED
  TCP    127.0.0.1:4999         kush-PC:5001           ESTABLISHED
  TCP    127.0.0.1:5001         kush-PC:4999           ESTABLISHED
  TCP    127.0.0.1:5208         kush-PC:5209           ESTABLISHED
  TCP    127.0.0.1:5209         kush-PC:5208           ESTABLISHED
  TCP    127.0.0.1:6751         kush-PC:895            ESTABLISHED
  TCP    127.0.0.1:27015        kush-PC:1036           ESTABLISHED
  TCP    192.168.2.5:2869       192.168.2.1:33040      TIME_WAIT
  TCP    192.168.2.5:7227       cs:ssh                 ESTABLISHED
  TCP    192.168.2.5:7312       blogger:http           ESTABLISHED
  TCP    192.168.2.5:7410       clients1:https         ESTABLISHED
  TCP    192.168.2.5:7411       clients1:http          ESTABLISHED
  TCP    192.168.2.5:7428       googleads:http         ESTABLISHED
  TCP    192.168.2.5:7429       googleads:http         ESTABLISHED
  TCP    192.168.2.5:7430       googleads:http         ESTABLISHED
  TCP    192.168.2.5:7432       googleads:http         ESTABLISHED
  TCP    192.168.2.5:7433       googleads:http         ESTABLISHED
  TCP    192.168.2.5:7434       googleads:http         ESTABLISHED
  TCP    192.168.2.5:7436       cr:http                ESTABLISHED
  TCP    192.168.2.5:7438       toolbarqueries:http    ESTABLISHED

= print the process tree or which process is connected to which process ?
ptree

output is the formatted tree showing parent and child spawning of process at different levels. A more precise implication is  "ptree PROCESS_ID".

= to show show directory size in kilobytes
du -k

= same as prstat what would you use to show io stats
iostat

simple but the output is difficult to analyse. The reads / sec, w / sec, kilo reads / sec, kilo writes / sec, more data to use show page faults, page in / out etc.

A good reference to look at would be Global Guide Line