Linux Administration Commands

top

The top command is probably the most useful one for an Oracle DBA managing a database on Linux. Say the system is slow and you want to find out who is gobbling up all the CPU and/or memory. To display the top processes, you use the command top.
Note that unlike other commands, top does not produce an output and sits still. It refreshes the screen to display new information. So, if you just issue top and leave the screen up, the most current information is always up. To stop and exit to shell, you can press Control-C.

$ top

18:46:13  up 11 days, 21:50,  5 users,  load average: 0.11, 0.19, 0.18 
151 processes: 147 sleeping, 4 running, 0 zombie, 0 stopped 
CPU states:  cpu    user    nice  system    irq  softirq  iowait    idle 
           total   12.5%    0.0%    6.7%   0.0%     0.0%    5.3%   75.2% 
Mem:  1026912k av,  999548k used,   27364k free,       0k shrd,  116104k buff 
                    758312k actv,  145904k in_d,   16192k in_c 
Swap: 2041192k av,  122224k used, 1918968k free                  590140k cached 
 
  PID USER     PRI  NI  SIZE  RSS SHARE STAT %CPU %MEM   TIME CPU COMMAND 
  451 oracle    15   0  6044 4928  4216 S     0.1  0.4   0:20   0 tnslsnr 
 8991 oracle    15   0  1248 1248   896 R     0.1  0.1   0:00   0 top 
    1 root      19   0   440  400   372 S     0.0  0.0   0:04   0 init 
    2 root      15   0     0    0     0 SW    0.0  0.0   0:00   0 keventd 
    3 root      15   0     0    0     0 SW    0.0  0.0   0:00   0 kapmd 
    4 root      34  19     0    0     0 SWN   0.0  0.0   0:00   0 ksoftirqd/0 
    7 root      15   0     0    0     0 SW    0.0  0.0   0:01   0 bdflush 
    5 root      15   0     0    0     0 SW    0.0  0.0   0:33   0 kswapd 
    6 root      15   0     0    0     0 SW    0.0  0.0   0:14   0 kscand 
    8 root      15   0     0    0     0 SW    0.0  0.0   0:00   0 kupdated 
    9 root      25   0     0    0     0 SW    0.0  0.0   0:00   0 mdrecoveryd
... output snipped ...

Let's examine the different types of information produced.

The first line:  18:46:13 up 11 days, 21:50, 5 users, load average: 0.11, 0.19, 0.18
shows the current time (18:46:13), that system has been up for 11 days; that the system has been working for 21 hours 50 seconds. The load average of the system is shown (0.11, 0.19, 0.18) for the last 1, 5 and 15 minutes respectively. (By the way, you can also get this information by issuing the uptime command.)
If the load average is not required, press the letter "l" (lowercase L); it will turn it off. To turn it back on press l again.  Ideally Load average should be less than 1, otherwise the processes are fully burdened

The second line:  151 processes: 147 sleeping, 4 running, 0 zombie, 0 stopped
shows the number of processes, running, sleeping, etc.

The third and fourth lines: 

CPU states:  cpu    user    nice  system    irq  softirq  iowait    idle 
           total   12.5%    0.0%    6.7%   0.0%     0.0%    5.3%   75.2%

show the CPU utilization details. The above line shows that user processes consume 12.5% and system consumes 6.7%. The user processes include the Oracle processes. Press "t" to turn these three lines off and on. If there are more than one CPU, you will see one line per CPU.

The next two lines:

Mem:  1026912k av, 1000688k used,  26224k free,    0k shrd,  113624k buff 
                    758668k actv,  146872k in_d,  14460k in_c
Swap: 2041192k av, 122476k used,   1918716k free             591776k cached

show the memory available and utilized. Total memory is "1026912k av", approximately 1GB, of which only 26224k or 26MB is free. The swap space is 2GB; but it's almost not used. To turn it off and on, press "m".

The rest of the display shows the processes in a tabular format. Here is the explanation of the columns:

Column Description
PID The process ID of the process
USER The user running the process
PRI The priority of the process
NI The nice value: The higher the value, the lower the priority of the task
SIZE Memory used by this process (code+data+stack)
RSS The physical memory used by this process
SHARE The shared memory used by this process
STAT

The status of this process, shown in code. Some major status codes are:
R – Running
S –Sleeping
Z – Zombie
T – Stopped

You can also see second and third characters, which indicate:
W – Swapped out process
N – positive nice value
%CPU The percentage of CPU used by this process
%MEM The percentage of memory used by this process
TIME The total CPU time used by this process
CPU If this is a multi-processor system, this column indicates the ID of the CPU this process is running on.
COMMAND The command issued by this process

While the top is being displayed, you can press a few keys to format the display as you like. Pressing the uppercase M key sorts the output by memory usage. (Note that using lowercase m will turn the memory summary lines on or off at the top of the display.) This is very useful when you want to find out who is consuming the memory. Here is sample output:

PID USER     PRI  NI  SIZE  RSS SHARE STAT %CPU %MEM   TIME CPU COMMAND 
31903 oracle    15   0 75760  72M 72508 S     0.0  7.2   0:01   0 ora_smon_PRODB2 
31909 oracle    15   0 68944  66M 64572 S     0.0  6.6   0:03   0 ora_mmon_PRODB2 
31897 oracle    15   0 53788  49M 48652 S     0.0  4.9   0:00   0 ora_dbw0_PRODB2

Now that you learned how to interpret the output, let's see how to use command line parameters.

The most useful is -d, which indicates the delay between the screen refreshes. To refresh every second, use top -d 1.

The other useful option is -p. If you want to monitor only a few processes, not all, you can specify only those after the -p option. To monitor processes 13609, 13608 and 13554, issue: 

top -p 13609 -p 13608 -p 13554

This will show results in the same format as the top command, but only those specific processes.


Tip for Oracle Users

It's probably needless to say that the top utility comes in very handy for analyzing the performance of database servers. Here is a partial top output.

20:51:14  up 11 days, 23:55,  4 users,  load average: 0.88, 0.39, 0.27 
113 processes: 110 sleeping, 2 running, 1 zombie, 0 stopped 
CPU states:  cpu    user    nice  system    irq  softirq  iowait    idle 
           total    1.0%    0.0%    5.6%   2.2%     0.0%   91.2%    0.0% 
Mem:  1026912k av, 1008832k used,   18080k free,       0k shrd,   30064k buff 
                    771512k actv,  141348k in_d,   13308k in_c 
Swap: 2041192k av,   66776k used, 1974416k free                  812652k cached 
 
  PID USER     PRI  NI  SIZE  RSS SHARE STAT %CPU %MEM   TIME CPU COMMAND 
16143 oracle    15   0 39280  32M 26608 D     4.0  3.2   0:02   0 oraclePRODB2...
    5 root      15   0     0    0     0 SW    1.6  0.0   0:33   0 kswapd
... output snipped ...

Let's analyze the output carefully. The first thing you should notice is the "idle" column under CPU states; it's 0.0%—meaning, the CPU is completely occupied doing something.
The question is, doing what?
Move your attention to the column "system", just slightly left; it shows 5.6%. So the system itself is not doing much.
Go even more left to the column marked "user", which shows 1.0%.
Since user processes include Oracle as well, Oracle is not consuming the CPU cycles.
So, what's eating up all the CPU?
The answer lies in the same line, just to the right under the column "iowait", which indicates 91.2%. This explains it all: the CPU is waiting for IO 91.2% of the time.

So why so much IO wait? The answer lies in the display. Note the PID of the highest consuming process: 16143. You can use the following query to determine what the process is doing: 

select s.sid, s.username, s.program
from v$session s, v$process p
where spid = &server_process_id
and p.addr = s.paddr
/
       SID USERNAME PROGRAM
------------------- -----------------------------
       159 SYS      rman@prolin2 (TNS V1-V3)

The rman process is taking up the IO waits related CPU cycles. This information helps you determine the next course of action.


skill and snice

From the previous discussion you learned how to identify a CPU consuming resource. What if you find that a process is consuming a lot of CPU and memory, but you don't want to kill it? Consider the top output below: 

$ top -c -p 16514

23:00:44  up 12 days,  2:04,  4 users,  load average: 0.47, 0.35, 0.31 
1 processes: 1 sleeping, 0 running, 0 zombie, 0 stopped 
CPU states:  cpu    user    nice  system    irq  softirq  iowait    idle 
           total    0.0%    0.6%    8.7%   2.2%     0.0%   88.3%    0.0% 
Mem:  1026912k av, 1010476k used,   16436k free,       0k shrd,   52128k buff 
                    766724k actv,  143128k in_d,   14264k in_c 
Swap: 2041192k av,   83160k used, 1958032k free                  799432k cached 
 
  PID USER     PRI  NI  SIZE  RSS SHARE STAT %CPU %MEM   TIME CPU COMMAND 
16514 oracle    19   4 28796  26M 20252 D N   7.0  2.5   0:03   0 oraclePRODB2...

Now that you confirmed the process 16514 is consuming a lot of memory, you can "freeze" it—but not kill it—using the skill command.

$ skill -STOP 1

After this, check the top output:

23:01:11  up 12 days,  2:05,  4 users,  load average: 1.20, 0.54, 0.38 
1 processes: 0 sleeping, 0 running, 0 zombie, 1 stopped 
CPU states:  cpu    user    nice  system    irq  softirq  iowait    idle 
           total    2.3%    0.0%    0.3%   0.0%     0.0%    2.3%   94.8% 
Mem:  1026912k av, 1008756k used,   18156k free,       0k shrd,    3976k buff 
                    770024k actv,  143496k in_d,   12876k in_c 
Swap: 2041192k av,   83152k used, 1958040k free                  851200k cached 
 
  PID USER     PRI  NI  SIZE  RSS SHARE STAT %CPU %MEM   TIME CPU COMMAND 
16514 oracle    19   4 28796  26M 20252 T N   0.0  2.5   0:04   0 oraclePRODB2...

The CPU is now 94% idle from 0%. The process is effectively frozen. After some time, you may want to revive the process from coma: 

$ skill -CONT 16514

This approach is immensely useful for temporarily freezing processes to make room for more important processes to complete.

The command is very versatile. If you want to stop all processes of the user "oracle", only one command does it all: 

$ skill -STOP oracle

You can use a user, a PID, a command or terminal id as argument. The following stops all rman commands.

$ skill -STOP rman

As you can see, skill decides that argument you entered—a process ID, userid, or command—and acts appropriately. This may cause an issue in some cases, where you may have a user and a command in the same name. The best example is the "oracle" process, which is typically run by the user "oracle". So, when you want to stop the process called "oracle" and you issue: 

$ skill -STOP oracle

all the processes of user "oracle" stop, including the session you may be on. To be completely unambiguous you can optionally give a new parameter to specify the type of the parameter. To stop a command called oracle, you can give: 

$ skill -STOP -c oracle

The command snice is similar. Instead of stopping a process it makes its priority a lower one. First, check the top output: 

  PID USER     PRI  NI  SIZE  RSS SHARE STAT %CPU %MEM   TIME CPU COMMAND 
    3 root      15   0     0    0     0 RW    0.0  0.0   0:00   0 kapmd 
13680 oracle    15   0 11336  10M  8820 T     0.0  1.0   0:00   0 oracle 
13683 oracle    15   0  9972 9608  7788 T     0.0  0.9   0:00   0 oracle 
13686 oracle    15   0  9860 9496  7676 T     0.0  0.9   0:00   0 oracle 
13689 oracle    15   0 10004 9640  7820 T     0.0  0.9   0:00   0 oracle 
13695 oracle    15   0  9984 9620  7800 T     0.0  0.9   0:00   0 oracle 
13698 oracle    15   0 10064 9700  7884 T     0.0  0.9   0:00   0 oracle 
13701 oracle    15   0 22204  21M 16940 T     0.0  2.1   0:00   0 oracle

Now, drop the priority of the processes of "oracle" by four points. Note that the higher the number, the lower the priority. 

$ snice +4 -u oracle

  PID USER     PRI  NI  SIZE  RSS SHARE STAT %CPU %MEM   TIME CPU COMMAND 
16894 oracle    20   4 38904  32M 26248 D N   5.5  3.2   0:01   0 oracle

Note how the NI column (for nice values) is now 4 and the priority is now set to 20, instead of 15. This is quite useful in reducing priorities.




Amount of RAM, hardware config


Check swap activity (Oracle Note 225451.1)
The recommended SWap size is two to three times the amount of Physical Memory for Swap space (unless the system exceeds 1 GB of Physical Memory, where two times the amount of Physical Memory for Swap space is sufficient)
Swap space in Linux is used when the amount of physical memory (RAM) is full.If the system needs more memory resources and the physical memory is full, inactive pages in memory are moved to the swap space. While swap space can help machines with a small amount of RAM, it should not be considered a replacement for more RAM. Swap space is located on hard drives, which have a slower access time than physical memory.
Swapping is one of the Unix mechanisms to accommodate the size limitation of memory by moving entire processes to disk to reclaim memory.
Paging is another Unix machanism to manage the limitations of memory. Unlike swapping, where entire processes are moved in and out of memory, paging moves only individual pages of processes to disk. Paging is not as serious a problem as swapping, as the entire program does not have to reside in memory to run. A small amount of paging may not noticeably affect the performance of a system. However, the performance of a system may degraderapidly as paging activity increases.
Swap space on disk is used to hold pages of memory that have been paged or swapped out. A shortage of swap space may cause symptoms such as system hanging, poor response times, and unsuccessful spawning of new processes.
Swap space can be a dedicated swap partition (recommended), a swap file, or a combination of swap partitions and swap files.
When analyzing your UNIX machine, make sure that the machine is not swapping at all and at worst paging lightly. This indicates a system with a healthy amount of memory available.

How can I enable Swap ?
First check is Swap is enabled:
/sbin/swapon -s

Filename Type Size Used Priority
/dev/hda3 partition 514072 2816 -1

To enable swap, check for swap entries in your /etc/fstab
grep swap /etc/fstab
/dev/hda3 swap swap defaults 0 0

and use the '/sbin/swapon -a' command to enable all Swap partitions listed in /etc/fstab.

How to add a swapfile?
A: Determine the size of the new swap file and multiple by 1024 to determine the block size.
For example, the block size of a 64 MB swap file is 65536.

At a shell prompt as root, type the following command with count being equal to the desired block size:
% dd if=/dev/zero of=/data2/swapfile1 bs=1024 count=65536

Setup the swap file with the command:
% /sbin/mkswap /data2/swapfile1

To enable the swap file immediately but not automatically at boot time:
% /sbin/swapon /data2/swapfile

To enable it at boot time, edit /etc/fstab to include:
/data2/swapfile swap swap defaults 0 0

The next time the system boots, it will enable the new swap file.


Check Services Running and stop them if not used
netstat
netstat -lt
netstat -m     Shows ports where they are running
netstat -tap | grep LISTEN   --> Shows currently running processes with PID and Program Name

Services that should be removed: r* (shell or rsh, login or rlogin, exec or rexec, rcp), telnet, ftp, sendmail, exim, postfix, printer, qmail, http, portmap, SMBD (Samba)

chkconfig --list        --> Show services running and its level
chkconfig --del servicename       --> Stop that service
chkconfig --level 345 servicename off      --> Stop that service for level 3,4,5

Also it could be necessary to check the file /etc/inetd.conf  because it has references to some services, if any service that I want to stop is there, comment that line and reboot the server or run
/etc/init.d/inetd restart


Enable FTP and TELNET Services
cd to /etc/xinetd.d
vi wu-ftpd
Change the disable field from "yes" to "no".
Save changes.
vi telnet
Change the disable field from "yes" to "no"
Save changes


OS version

OS kernel parameters files (<note:68862.1>)
Max number of semaphores sets (SEMMNI)

Max number of semaphores systemwide (SEMMNS)

Max number of shared segments
Max shared segment size

Max number of open files per user/system wide =  more /proc/sys/fs/file-nr
The three values in file-nr denote the number of allocated file handles, the number of free file handles and the maximum number of file handles. The number of free file handles is counted out of the number of allocated file handles. This means, that the number of used file handles is (allocated-free) and at any given time, one can open up to (maximum-(allocated-free)) additional file handles. If this number gets close to zero, you probably want to increase the maximum, by writing to file-max, or you'll start getting errors when programs try to open files.


Using PMAP to determine the memory size of background processes
First, to determine the memory size, the process id (PID) of the  Oracle background process must be found. This is done by issuing the following command: 
% ps -ef |grep SID
  oracle 18523     1  0 00:07:03 ?        0:13 oracleDEVSOL (LOCAL=NO)
  oracle 15237     1  0 09:21:27 ?        0:12 oracleDEVSOL (LOCAL=NO)
  oracle   682     1  0   Jun 25 ?        0:06 oracleDEVSOL (LOCAL=NO)
  oracle 16544     1  0 14:25:53 ?        0:00 oracleDEVSOL (LOCAL=NO)
  oracle 19326     1  0 06:49:13 ?        0:00 oracleDEVSOL (LOCAL=NO)
  oracle   532     1  0   Jun 25 ?        0:01 ora_pmon_DEVSOL
  oracle   534     1  0   Jun 25 ?       27:33 ora_dbw0_DEVSOL
  oracle   536     1  0   Jun 25 ?       47:12 ora_lgwr_DEVSOL
  oracle   538     1  0   Jun 25 ?        3:39 ora_ckpt_DEVSOL
  oracle   540     1  0   Jun 25 ?        1:55 ora_smon_DEVSOL
  oracle   542     1  0   Jun 25 ?        0:00 ora_reco_DEVSOL
  oracle   544     1  0   Jun 25 ?        0:20 ora_cjq0_DEVSOL
  oracle   546     1  0   Jun 25 ?        2:40 ora_qmn0_DEVSOL
  oracle   548     1  0   Jun 25 ?        0:00 ora_s000_DEVSOL
  oracle   550     1  0   Jun 25 ?        0:00 ora_d000_DEVSOL
  oracle   555     1  0   Jun 25 ?        0:44 ora_p000_DEVSOL
  oracle   557     1  0   Jun 25 ?        0:40 ora_p001_DEVSOL
  oracle   559     1  0   Jun 25 ?        1:04 ora_p002_DEVSOL
  oracle   561     1  0   Jun 25 ?        2:53 ora_p003_DEVSOL
 
 Second, enter the following command:
pmap -x  540  (540 is the PID for the SMON process) 
         Address   Kbytes Resident Shared Private Permissions       Mapped File
0000000100000000   50472   23640   21336    2304 read/exec         oracle
0000000103248000     712     512     368     144 read/write/exec   oracle
00000001032FA000     392     208       -     208 read/write/exec     [ heap ]
0000000380000000 1462272 1462272       - 1462272 read/write/exec/shared  [ ism shmid=0x65 ]
FFFFFFFF7CE70000      72      72       -      72 read/write          [ anon ]
FFFFFFFF7CE88000      32      16       -      16 read/write          [ anon ]
FFFFFFFF7CF00000       8       8       -       8 read/write          [ anon ]
FFFFFFFF7CF10000       8       8       -       8 read/write          [ anon ]
FFFFFFFF7CF50000     136     128       -     128 read/write          [ anon ]
FFFFFFFF7CF74000      48      40       -      40 read/write          [ anon ]
FFFFFFFF7D000000       8       -       -       - read/write/exec     [ anon ]
FFFFFFFF7D100000      16      16       8       8 read/exec         libc_psr.so.1
FFFFFFFF7D200000      16      16       8       8 read/exec         libmp.so.2
FFFFFFFF7D304000       8       8       -       8 read/write/exec   libmp.so.2
FFFFFFFF7D400000      88      72      64       8 read/exec         libm.so.1
FFFFFFFF7D516000       8       8       -       8 read/write/exec   libm.so.1
FFFFFFFF7D600000       8       8       -       8 read/write/exec     [ anon ]
FFFFFFFF7D700000       8       8       -       8 read/exec         libkstat.so.1
FFFFFFFF7D802000       8       8       -       8 read/write/exec   libkstat.so.1
FFFFFFFF7D900000      32      32      24       8 read/exec         librt.so.1
FFFFFFFF7DA08000       8       8       -       8 read/write/exec   librt.so.1
FFFFFFFF7DB00000      32      32      24       8 read/exec         libaio.so.1
FFFFFFFF7DC08000       8       8       -       8 read/write/exec   libaio.so.1
FFFFFFFF7DD00000     704     600     504      96 read/exec         libc.so.1
FFFFFFFF7DEB0000      56      56       -      56 read/write/exec   libc.so.1
FFFFFFFF7DEBE000       8       8       -       8 read/write/exec   libc.so.1
FFFFFFFF7E000000      32      24       8      16 read/exec         libgen.so.1
FFFFFFFF7E108000       8       8       -       8 read/write/exec   libgen.so.1
FFFFFFFF7E200000      56      40      32       8 read/exec         libsocket.so.1
FFFFFFFF7E30E000      16      16       -      16 read/write/exec   libsocket.so.1
FFFFFFFF7E400000    5328    1864    1736     128 read/exec         libjox9.so
FFFFFFFF7EA32000     384     288       -     288 read/write/exec   libjox9.so
FFFFFFFF7EA92000       8       -       -       - read/write/exec   libjox9.so
FFFFFFFF7EB00000       8       8       -       8 read/write/exec     [ anon ]
FFFFFFFF7EC00000     656     224     216       8 read/exec         libnsl.so.1
FFFFFFFF7EDA4000      56      56       -      56 read/write/exec   libnsl.so.1
FFFFFFFF7EDB2000      40       -       -       - read/write/exec   libnsl.so.1
FFFFFFFF7EE00000      32      24       8      16 read/exec         libskgxn9.so
FFFFFFFF7EF06000       8       8       -       8 read/write/exec   libskgxn9.so
FFFFFFFF7F000000       8       8       -       8 read/write/exec     [ anon ]
FFFFFFFF7F100000       8       8       -       8 read/exec         libskgxp9.so
FFFFFFFF7F200000       8       8       8       - read/write/exec   libskgxp9.so
FFFFFFFF7F300000       8       8       -       8 read/exec         libodmd9.so
FFFFFFFF7F400000       8       8       8       - read/write/exec   libodmd9.so
FFFFFFFF7F500000       8       8       -       8 read/exec         libdl.so.1
FFFFFFFF7F600000     128     128     120       8 read/exec         ld.so.1
FFFFFFFF7F71E000       8       8       -       8 read/write/exec   ld.so.1
FFFFFFFF7F720000       8       8       -       8 read/write/exec   ld.so.1
FFFFFFFF7FFDC000     144     120       -     120 read/write          [ stack ]
----------------  ------  ------  ------  ------
        total Kb 1522136 1490664   24472 1466192

The private memory of this SMON process is 1466192K minus the SGA size  which is the line marked with 'shmid=' above. In this case it is 1462272K.
The calculation is as follows:  1466192K minus 1462272K is 3920K. 
So, the process  memory for SMON is 3920K.



TCP keepalive parameters

TCP tuning parameters

Process Limits (<note:188149.1>) ulimit -a

Display system/error messages = dmesg

OS kernel parameters values = ipcs -l

Am I on a 32 or 64 bit OS? = more /proc/cpuinfo



General Performance

vmstat 5 3 ( = This utility provides a report that covers process activity, paging, memory usage, disk I/O, and CPU usage (also you can use xosview). When analyzing your UNIX machine, make sure that the machine is not swapping at all and at worst paging lightly.
If US + SY near 100 operating at full capacity

procs                      memory      swap          io     system         cpu
 r  b   swpd   free   buff  cache   si   so    bi    bo   in    cs us sy id wa
 0  0 329476  54880  91600 613852    0    1     4     2    0     0  1  1  3  1
 0  0 329476  54560  91600 613852    0    0     0    36  118   128 25  0 74  0
 0  0 329476  54564  91600 613860    0    0     1    48  127   143 25  0 74  1


Here there are NO pageouts (po or so) occurring on this system. It is OK and normal to have page out (po or so) activity. You should get worried when the number of page ins (pi or si) starts rising. This indicates that you system is starting to page
There are no processes that are waiting to be run (r), blocked (b), or waiting for IO (w) in the RUN QUEUE (When a process is ready to be processed by a CPU it will be placed on the waiting line or RUN-QUEUE). You want to keep the RUN-QUEUE under 5-6 for a single CPU machine.

Having any processes in the b or w columns is a sign of a problem system.
Having an id of 0 is a sign that the cpu is overburdoned.
Having high values in pi and po show excessive paging.

  
free = To check amount of memory and if exists or not swapping activity    
 
sar -b  = To check physical disk I/O activity or buffer Activity

CPU Usage

sar -u 10 5 (10 seconds apart; 8 times):= Reports CPU Utilization. Nice column is the priority of that process, bigger numbers less priority
13:10:56 %usr %sys %wio %idle
13:11:02  51   5        3       42
13:11:07  45   7        16     32
13:11:12  51   4         1      43
13:11:18  51   8         7      34
13:11:23  52   13       3      32
%usr: Percent of CPU in user mode
%sys: Percent of CPU in system mode
%wio: Percent of CPU running idle with a process waiting for block I/O
%idle: Percent of CPU that is idle

Once it is established that the system has high CPU usage, the next step is to find out who is using the CPU.
Ps -fe | grep smon
or
ps -e -o pcpu -o pid -o user -o args | sort -k 1 | tail -21r
Displays the top 10 CPU users on the system.

 UID      PID   PPID   C STIME TTY TIME CMD <-- Label added for clarity.
usupport 28180 1      0 Oct 31 - 0:48  ora_smon_V734
usupport 30262 1      0 Nov 01 - 0:00  ora_smon_VKHILL
usupport 30900 1      0 Oct 14 - 9:03  ora_smon_V806
usupport 31958 1    111 Oct 24 - 3:31  ora_smon_V815 <-- Notice the C column
usupport 37986 1      0 Nov 06 - 14:00 ora_smon_V805

Here we can see a smon of the database V815 using a lot of CPU by looking at the C column which reflects the CPU units of processing that are being used.
There are 100 units per CPU so The reason why this number is above 100 is that this machine has 2 cpus.

% /usr/sbin/bindprocessor -q
The available processors are: 0 1

sysctl
Configurar los paràmetros del kernel en tiempo de ejuecución.
Ejemplos: sysctl -a


adduser
añadir usuario de sistema.
Ejemplos: adduser pepe, adduser -s /bin/false pepe

userdel
eliminar usuario de sistema
Ejemplos: userdel pepe

usermod
modificar usuario de sistema
Ejemplos: usermod -s /bin/bash pepe

df
disk free. espacio en disco disponible. Muy util.
Ejemplos: df, df -h

uname
Informacion sobre el tipo de unix en el que estamos, kernel, etc.
Ejemplos: uname, uname -a

netstat
la informacion sobre las conexiones de red activas.
Ejemplos: netstat, netstat -ln, netstat -l, netstat -a

traceroute

herramienta de red que nos muestra el camino que se necesita para llegar a otra maquina.
Ejemplos: traceroute www.rediris.es

du
disk use. uso de disco. Muestra el espacio que esta ocupado en disco.
Ejemplos: du *, du -sH /*, du -sH /etc

ifconfig
On Linux systems, the ethernet device is typically called eth0. In order to find the MAC address of the ethernet device, you must first become root, through the use of su. Then, type ifconfig -a and look up the relevant info.
For example:
# ifconfig -a eth0
Link encap:Ethernet HWaddr 00:60:08:C4:99:AA
inet addr:131.225.84.67 Bcast:131.225.87.255 Mask:255.255.248.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:15647904 errors:0 dropped:0 overruns:0
TX packets:69559 errors:0 dropped:0 overruns:0
Interrupt:10 Base address:0x300
The MAC address is the HWaddr listed on the first line.
In the case of this machine, it is 00:60:08:C4:99:AA.

route
gestiona las rutas a otras redes.
Ejemplos: route, route -n

iptraf
muestra en una aplicacion de consola TODO el trafico de red IP, UDP, ICMP.
Permite utilizar filtros, y es SUMAMENTE UTIL para diagnostico y depuracion de firewalls
Ejemplos: iptraf

tcpdump
vuelca el contenido del trafico de red.
Ejemplos: tcpdump, tcpdump -u

lsof
muestra los ficheros(librerias, conexiones) que utiliza cada proceso
Ejemplos: lsof, lsof -i, lsof | grep fichero

lsmod
Muestra los modulos de kernel que estan cargados.
Ejemplos: lsmod

modprobe
Trata de instalar un modulo, si lo encuentra lo instala pero de forma temporal.
Ejemplos: modprobe ip_tables, modprobe eepro100

rmmod
Elimina modulos del kernel que estan cargados
Ejemplos: rmmod <nombre de modulo>

sniffit
Sniffer o husmeador de todo el trafico de red. No suele venir instalado por defecto.
Ejemplos: sniffit -i

who
El comando "who" informa de los usuarios que se hallan presentes en el sistema




Managing Packages

See the list of installed packages
rpm -qa


How do I remove the old kernel and keep only the latest kernel?
# rpm -q kernel

To see what packages are installed. Then e.g. remove one (or several at once):
# rpm -e kernel-2.4.18-10  kernel-2.4.18-14


Metalink Notes on Linux


note:265262.1       Oracle on Linux Full Library
note:270683.1       Pre Install checks for the Oracle Application Server 10g (9.0.4) on Linux Platforms
note:263715.1       Configuring RHAS 30 for Usage with Oracle
note:184821.1       Step-By-Step Installation of 9.2.0.4 RAC on Linux
bug:3016968         Asyncio Functionality Is Not Working On RHEL 3 With 10g
note:1037322.6     WHAT IS THE DB_FILE_MULTIBLOCK_READ_COUNT PARAMETER?
note:68633.1         Init.ora Parameter "SORT_MULTIBLOCK_READ_COUNT" Reference
note:39023.1         Init.ora Parameter "HASH_MULTIBLOCK_IO_COUNT" Reference Note
note:47324.1         PARAMETER:DB_FILE_DIRECT_IO_COUNT
note:225751.1       Asynchronous I/O (aio) on RedHat Advanced Server - FAQ