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Linux for the Oracle DBA for more tips and tricks.
One of the most confounding issues for the UNIX neophyte is being
confronted with a complex UNIX command. The cryptic nature of UNIX
is such that even the most seasoned UNIX professional may have
trouble deciphering the purpose of the command.
We will begin by
examining a cryptic UNIX command and then see how the command is
deciphered by applying a simple set of rules.
Decomposing a UNIX
Script
One of the most foreign concepts for the UNIX neophyte is
the ability of the UNIX programmer to string commands together into
a powerful one-line script. Below we see a one-line UNIX script
that perform an important Oracle function:
ps -ef|grep "ora_"|grep
-v grep|awk '{ print $2 }'|-exec rm –f {} \;
At first glance, this
powerful UNIX command appears to be a conglomeration of cryptic
letters. However, upon closer examination we see that this UNIX
command is actually a series of commands that are joined together
with the "pipe" operator "|".
When viewed this way, our command can
be viewed as a connected list of commands:
ps –ef
|
grep "ora_"
|
grep -v grep
|
awk '{ print $2 }'
|
-exec rm –f {} \;
In this
sense, we can examine each command, one at a time, and see how each
successive commands refines the output from the prior UNIX command.
Once we see the individual commands that comprise the UNIX script,
we are ready to begin building the command from each component.
Deciphering UNIX Command Syntax
In this example, we are examining a
UNIX script to kill all Oracle background processes for a database.
There are times when it is necessary to kill all Oracle processes
or a selected set of Oracle processes.
This is a common UNIX script
used by an Oracle DBA who wants to kill all Oracle processes when
the database is "locked-up" and he cannot enter server manager to
gently stop the database.
The basic format of the UNIX kill
command is:
Kill –9 PID1 PID2 PID3
(where PIDn is a list of UNIX
process ID's)
To kill all Oracle processes we issue the
following command:
ps -ef|grep "ora_"|grep -v grep|awk
'{print $2}'|-exec kill -9 {} \;
Let's look at how it works:
- The ps –ef UNIX command displays all active processes on the
server. However, we want to limit our command to only those
processes that are related to the Oracle database.
- The "grep
"ora_" command removes all but the Oracle background processes:
>ps -ef|grep "ora_"
oracle 13022 1 0 May 07 - 0:18
ora_db02_vald
oracle 14796 42726 0 09:00:46 pts/0 0:00 grep
ora_
oracle 17778 1 0 May 07 - 0:14 ora_smon_devp
oracle 18134 1 0 May 07 - 0:37 ora_snp1_vald
oracle 19516 1 0 May 07 - 0:24 ora_db04_prod
oracle 21114 1 0 May 07 - 0:37 ora_snp0_devp
oracle 28436 1 0 May 07 - 0:18 ora_arch_prod
- The "grep –v grep" removes our grep command, so we don't
kill our own process. The grep –v is the opposite of grep,
whereas grep find strings, grep –v excludes strings. Note that
the grep line is now missing from our output. Another
alterative to using grep -v is to enclose the target in square
brackets (e.g. ps -ef|grep [p]mon) this has the same
functionality as the grep -v grep syntax and removes the grep
line:
>ps -ef|grep "ora_"|grep -v grep
oracle 13022 1 0 May 07 - 0:18 ora_db02_vald
oracle
17778 1 0 May 07 - 0:14 ora_smon_devp
oracle
18134 1 0 May 07 - 0:37 ora_snp1_vald
oracle
19516 1 0 May 07 - 0:24 ora_db04_prod
oracle
21114 1 0 May 07 - 0:37 ora_snp0_devp
oracle
28436 1 0 May 07 - 0:18 ora_arch_prod
- We now
use the awk command to get the Process ID (PID) for these
processes. The "awk '{print $2}'" command only displays the PID
column:
>ps -ef|grep "ora_"|grep -v grep|awk '{ print $2 }'
13022
17778
18134
19516
21114
28436
28956
- Now we have a list
of process ID's for the Oracle background processes. Finally, we
"pipe" the list of PID's to the kill command with "-exec" command.
(Note that HP/UX and AIX also have an "xargs" command for this
purpose.
ps -ef|grep "ora_"|grep -v grep|awk '{ print $2 }'|-exec
rm –f {} \;
- Now that our script is created we can assign it to
a UNIX "alias" so we can issue the script in a simple command.
Below, we assign our script to the alias nuke_oracle:
alias
nuke_oracle = "ps -ef|grep "ora_"|grep -v grep|awk '{ print $2
}'|-exec rm –f {} \;"
Now, entering the alias nuke_oracle will
kill all Oracle background processes. Of course, we would never
risk assigning such a powerful command to an alias in the
real-world. Next, let's create another powerful UNIX script.
Building Commands into Scripts
Now that we know that the "-exec" and
"xargs" commands will apply a single UNIX command to a list of
inputs, let's look at how we can quickly generate a UNIX script to
perform a powerful task.
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