The oratab file is normally located in /etc or /var/opt/oracle. Origianally it was used for SQL*Net V1. It contains comments in unix-style leading pound signs (#), and data lines consisting of entries in this format:
database_sid:oracle_home_dir:Y|N
where database_sid is the system id (sid) of one of your oracle instances on this server. oracle_home_dir is the ORACLE_HOME directory associated with this instance. The Y|N flags indicate if the instance should automatically start at boot time (Y) or not (N).
You might think that if you are no longer running SQL*Net V1, you do not need oratab. However, Oracle's dbstart and dbshut scripts still use this file to figure out (using the third field, YorN) which instances are to be start up or shut down. And some other people (including me) have written scripts that cycle through multiple instances using oratab. But if you don't use SQL*Net V1, and don't use these scripts, you don't really need this file anymore.
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How does one prepare the Oracle environment?
An oraenv script is provided with every Oracle installation. Run it as part of your current environment to set the necessary environment variables like ORACLE_HOME, ORACLE_SID, etc. Never set the Oracle Home directory explicitely in a script.
The following example shows how to use oraenv (noninteractively) from a script:
export ORACLE_SID=ORCL;
export ORAENV_ASK=NO
. oraenv
NOTE: the ". " in front of "oraenv" is needed to run the script as part of the current shell.
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How do I get Oracle to automatically start when my server boots up?
Make sure the entry for your database SID in the /etc/oratab file ends in a capital Y. Eg:
# $ORACLE_SID:$ORACLE_HOME:[N|Y]
#
ORCL:/u01/app/oracle/product/8.0.5:Y
#
The scripts for starting and stopping databases are: $ORACLE_HOME/bin/dbstart and dbshut. SQL*Net (or Net8) is started with the lsnrctl command. Add the following entries to your /etc/rc2.d/S99dbstart (or equivalent) file:
su - oracle -c "/path/to/$ORACLE_HOME/bin/dbstart" # Start DB's
su - oracle -c "/path/to/$ORACLE_HOME/bin/lsnrctl start" # Start listener
su - oracle -c "/path/tp/$ORACLE_HOME/bin/namesctl start" # Start OraNames (optional)
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How does one list all installed products?
One can display all installed products with version information by executing the following commands:
cd $ORACLE_HOME/orainst
./inspdver
NOTE: From oracle 8i the "inspdver" command is not available anymore. If you find an alternative, please let us know.
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Can I export directly to a tape drive?
Yes, just use the tape device instead of the file name. Eg:
exp userid/password file=/dev/rmt0 table=emp volsize=1.2G
Note: The volume size is a number ending with a m, k, or b (M, K, or B). The default is bytes.
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Can I archive directly to tape?
Yes, set log_archive_dest = /dev/rmt0:100M in your init.ora file.
You can also use ARCHMON which communicates with ARCH. When the end of tape is reached, ARCH stops and signals ARCHMON to prompt the user for a new tape. When ARCHMON knows the tape is mounted, it tells ARCH to resume the archiving operation. It needs regular operator monitoring.
$ archmon @P:TEST
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I don't have enough space to export my database! Any suggestions?
Well, if you can't afford to buy extra disk space you can run export and compress simultaneously. This will prevent the need to get enough space for both the export file AND the compressed export file. Eg:
# Make a pipe
mknod expdat.dmp p # or mkfifo pipe
# Start compress sucking on the pipe in background
compress <> expdat.dmp.Z &
# Wait a second or so before kicking off the export
sleep 5
# Start the export
exp scott/tiger file=expdat.dmp
Or export accross the network directly into the target database:
Host A:
mknod FIFO.dmp p
exp u/p FILE=FIFO.dmp rest_of_parameters...
Host B:
mknod FIFO2.dmp p
rsh host1 dd if=FIFO.dmp > FIFO2.dmp &
imp u/p FILE=FIFO2.dmp rest_of_parameters...
Note:
It is important that you verify that the named pipe is ready on each side before you start the process.
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How can I overcome the Unix 2 Gig file limit?
This example uses the Unix split command to create multiple files, each smaller than the Unix (and imp/exp) 2 Gigabyte file size limit. This method would typically be used for import, export and SQL*Loader operations.
cd /tmp/data
rm exp.dmp
mknod exp.dmp p # mkfifo on certain Unix flavours
split -b2047m exp scott/tiger file=/tmp/data/exp.dmp record=n tables=tableX
cd /tmp/data
rm exp.dmp
mknod exp.dmp p
cat xaa xab xac xad >/tmp/data/exp.dmp &
imp scott/tiger file=/tmp/data/exp.dmp commit=y tables=tableX
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How can I export/import my database faster?
The IMP/EXP programs run in two task mode to protect the SGA from potential corruption by user programs. If you relink these programs in single task mode you can gain much improvement in speed (up to 30%). Although Oracle won't support this they supposedly use this method themselves.
Although running in single-task is faster, it requires more memory since the Oracle executable's text is no longer shared between the front-end and background processes. Thus, if you need to transfer large amounts of data between databases, relink the executale for greater efficiency.
cd $ORACLE_HOME/rdbms/lib
make -f ins_rdbms.mk singletask
# make -f ins_rdbms.mk expst
# make -f ins_rdbms.mk impst
# make -f ins_rdbms.mk sqlldrst
# mv expst $ORACLE_HOME/bin/
# mv impst $ORACLE_HOME/bin/
# mv sqlldrst $ORACLE_HOME/bin/
Now use expst and impst instead of imp or exp.
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How can I SELECT a value from a table into a Unix variable?
You can select a value from a database column directly into a Unix shell variable. Look at the following shell script examples:
#!/bin/sh
VALUE=`sqlplus -silent "user/password@instance" <
select max(c1) from t1;
exit;
END`
if [ -z "$VALUE" ]; then
echo "No rows returned from database"
exit 0
else
echo $VALUE
fi
Second example, using the SQL*Plus EXIT status code:
#!/bin/ksh
sqlplus -s >junk1 "usr/psw@instance" <
select count(*) num_rows
from table_name;
exit num_rows
EOF
echo "Number of rows are: $?"
Yet another example, only this time we will read multiple values from SQL*Plus into shell variables.
sqlplus -s usr/psw@instance |& # Open a pipe to SQL*Plus
print -p -- 'set feed off pause off pages 0 head off veri off line 500'
print -p -- 'set term off time off'
print -p -- "set sqlprompt ''"
print -p -- "select sysdate from dual;"
read -p SYSDATE
print -p -- "select user from dual;"
read -p USER
print -p -- "select global_name from global_name;"
read -p GLOBAL_NAME
print -p -- exit
echo SYSDATE: $SYSDATE
echo USER: $USER
echo GLOBAL_NAME: $GLOBAL_NAME
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How can I SELECT information into my vi-file?
When using vi to edit SQL*Plus or Pro*C code, sometimes one need to insert a table definition or data values into the file. You can simply open a new line, put 'desc EMP' (or a SELECT statement) into it and type:
:.,.!sqlplus -s /
... automagically output from your statement arrives in the vi buffer for cutting and pasting. You might even like to consider piping the output through grep, awk, sed or perl.
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How can I automate my on-line backup's?
Write a CRON job to:
1. Get the tablespace names from Oracle:
SELECT TABLESPACE_NAME FROM SYS.DBA_TABLESPACES;
2. Put the tablespaces in backup mode:
ALTER TABLESPACE ... BEGIN BACKUP;
3. Get the database file names from Oracle:
SELECT NAME FROM SYS.V_$DATAFILE;
SELECT NAME FROM SYS.V_$CONTROLFILE;
SELECT MEMBER FROM SYS.V_$LOGFILE;
4. Backup the files using pax, tar, ufsdump, dd, cpio or whatever file copy command you fancy. Note that if your database is on a raw partition, you can only use dd. Some examples:
$ find . -depth -print | cpio -ocBv >/dev/tapedevice
$ dd if=/dev/raw_device of=/dev/tape_device BS=8k
$ pax -w -f archive.pax *
5. End backup mode for all the tablespaces.
ALTER TABLESPACE ... END BACKUP;
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What is the purpose of the sgadef.dbf file?
The sgadef.dbf file can be found in the ${ORACLE_HOME}/dbs directory. Whatever you do, DO NOT REMOVE IT!!! It tells the oracle shadow process the address of the SGA when the process first connects to the database. If the process cannot find this file, it assumes the database is down.
Problems can arise when the reverse is true ie. the database is down but the sgadef file exists, as happens when the system crashes. In this case, the memory segment addressed in the file doesn't exist (try ipcs -m to convince yourself), which results in an error.
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Can I see what patches are applied to Oracle?
With the Unix "what" command one can see what patches are applied to an executable. The Oracle implementation of what is called owhat.
The 'what' command delves into a file and extracts SCCS version control information from that file, if any exists. For more details, look up 'man what'. Look at this example:
$ cd $ORACLE_HOME/bin
$ owhat oracle
Oracle patches in /app/oracle/product/7.3.4/bin/oracle:
sf.c VLFS patch 08/1/96
sksa.c VLFS patch 08/1/96
sp.c VLFS patch 08/1/96
ssf.c VLFS patch 08/1/96
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How does one monitor and trace Unix processes?
To trace what a Unix process is doing enter:
truss -rall -wall -p
truss -p $ lsnrctl dbsnmp_start
NOTE: The "truss" command works on SUN and Sequent. Use "strace" on Linux. If your operating system doesn't support the truss and strace commands, call your system administrator to find the equivalent command on your system.
Monitor your Unix system:
Unix message files record all system problems like disk errors, swap errors, NFS problems, etc. Monitor the following files on your system to detect system problems:
tail -f /var/adm/SYSLOG
tail -f /var/adm/messages
tail -f /var/log/syslog
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How does one write a script to do work on all DB's?
All databases on your machine should be listed in the /etc/oratab file. You can use this information to do processing on all databases on your machine. Look at this example:
#!/bin/ksh
ALL_DATABASES=`cat /etc/oratab|grep -v "^#"|grep -v "N$"|cut -f1 -d: -s`
for DB in $ALL_DATABASES
do
unset TWO_TASK
export ORACLE_SID=$DB
export ORACLE_HOME=`grep "^${DB}:" /etc/oratab|cut -d: -f2 -s`
export PATH=$ORACLE_HOME/bin:$PATH
echo "---> Database $ORACLE_SID, using home $ORACLE_HOME"
sqlplus -s system/${DB}password @<<-EOF
select * from global_name;
exit;
EOF
done
NOTE: The terminating 'EOF' should normally be in column 1. The '-' before the first EOF above causes the shell to strip all leading TAB characters (not spaces, only TABs) from that point until (and including the EOF). This lets you indent the code in between using TABs.
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Can one prevent passwords from appearing in the process table?
One can prevent Oracle passwords from showing in the Unix process table (ps -ef) when running an Oracle utility (like sqlplus). Look at the following solutions:
sqlplus /NOLOG @conn.sql
# No messing with ps, no password leak, connect from witin conn.sql
or...
echo "Name : \c"
read Name
echo "Password : \c"
stty -echo
read Password
stty echo
echo ${Name}/${Password} | sqlplus
or...
USER=scott
PASSWORD=tiger
{ echo ${USER}/${PASSWORD}; cat ${your_script_name_here}; } | sqlplus
PS: You can also create OPS$... or IDENTIFIED EXTERNALLY users in the database (to use OS authentication) and connect with a /
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Why doesn't Oracle release file space when you drop a tablespace?
Sometimes when you drop a tablespace within Oracle, then remove (rm) the underlying data files, Oracle will not release filesystem space until you shut it down. This can be confirmed with the "df -k" command.
This is normal behaviour on Unix machines. If a process has a file open for use, the file will be removed, but the space it occupies will remain in place until all processes referencing it are closed.
Use the "fuser" command before deleting Oracle datafiles. If any processes are touching them, you will not get the space back when you rm the file. If SMON is locking your file, just wait a few minutes until it releases it.
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How does one relink the Oracle Server executables?
Enter the following Unix commands:
cd $ORACLE_HOME/rdbms/lib
make -f ins_rdbms.mk install
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Can one copy the Oracle software from machine to machine?
Yes, you can copy or FTP the Oracle Software between similar machines. Look at the following example:
# use tar to copy files and directorys with permissions and ownership
tar cf - $ORACLE_HOME | rsh "cd $ORACLE_HOME; tar xf -"
To copy the Oracle software to a different directory on the same server:
cd /new/oracle/dir/
( cd $ORACLE_HOME; tar cf - . ) | tar xvf -
NOTE: Remember to relink the Intelligent Agent on the new machine to prevent messages like "Encryption key supplied is not the one used to encrypt file":
cd /new/oracle/dir/
cd network/lib
make -f ins_agent.mk install
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What should I do with those core files?
Make sure the complete CORE file was written out. System administrators usually limit core size to avoid dangerous core files filling file systems. Core file size can be limited with the "ulimit" or "limit" commands. Look at these examples:
$ ulimit -a # Display limits for your session under sh or ksh
$ limit # Display limits for your session under csh or tcsh
$ ulimit -c SIZE_IN_BLOCKS # Limit core size under sh or ksh
$ limit coredumpsize SIZE_IN_KB # Limit core size under csh or tcsh
If you see a core file lying around, just type "file core" to get some details about it. Example:
$ file core
core:ELF-64 core file - PA-RISC 2.0 from 'sqlplus' - received SIGABRT
Run the Unix process debugger for details. These details are normally requested by Oracle for in-depth analysis of your problem.
Solaris, HP-UX, etc:
$ adb
$c
$q
Sequent:
$ debug -c core $ORACLE_HOME/bin/sqlplus
debug> stack
debug> quit
Note: Some Unix operating systems use commands like sdb, xdb, dbx, etc. The same principles apply. Do a man on the command and just do it!
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What Environment Variables needs to be set?
Here are a few basic ORACLE environment variables. For more environment variables, please refer to the reference guides.
To check the value of these environment variables enter:
env | grep -e ORA -e TNS
LD_LIBRARY_PATH Path to library files. Eg: /usr/lib:/usr/openwin/lib:$ORACLE_HOME/lib:/usr/games/lib
ORACLE_BASE Full path name to the base directory for all versions of Oracle products.
ORACLE_HOME Full path name to the version of ORACLE you are currently using. ORACLE_HOME is normally found beneath ORACLE_BASE in the directory tree. This variable is used to find executable programs and message files.
ORACLE_SID ORACLE Server system identifier (SID) or instance name. The database name is used as ORACLE_SID. This is required for all ORACLE products and is set by the coraenv script.
ORACLE_PATH Defines the path names to locate files. If ORACLE_PATH is set, the application searches the directories specified by $ORACLE_PATH first, then the current directory. If ORACLE_PATH is not set, then the application uses the current directory. This variable is used by SQL*Plus, Forms and Menu.
ORACLE_TERM Defines a terminal definition. If not set, it defaults to the value of your TERM environment variable. Used by all character mode products.
ORAENV_ASK This will not ask for ORACLE_SID, it will take it as it is specified. This variable is normally set to "NO" before oraenv is invoked from a script.
TNS_ADMIN Defines the path name to the TNS (Transparent Network Substrate) files like TNSNAMES.ORA, SQLNET.ORA etc.
ORACLE_TRACLE Trace Oracle's Unix shell scripts as they execute (using set -x).
TWO_TASK The TWO_TASK environment variable specifies a SQL*Net connect string for connecting to a remote machine in a client/server configuration. SQL*Net will check the value of TWO_TASK and automatically add it to your connect string.
For example the following are equivalent:
sqlplus scott/tiger@db1
and
export TWO_TASK=db1; sqlplus scott/tiger
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What Unix commands can be used when administrating my database?
The Unix command set is so rich that I can never list them all, however, if you are a beginner, you may find the following commands useful. To get a detailed description of any command, just type man command-name.
cd Change the current directory. When you log in, you are in your "home" directory
ls List files in a directory (like the DOS DIR command)
pwd Print working (current) directory
cp Copy (duplicate) a file or directory
rm Remove (delete) a file. Note that rm is permanent, there is no undelete. Be careful "rm -r *" is an easy way to get fired!!!
mv Move or rename a file or directory. Works like cp except the old file is deleted
mkdir Creates a new (sub) directory
rmdir Remove a directory
chmod Change file permissions or access attributes
man UNIX manual pages
du Disk usage
script out.log Write everything printed on your terminal to file out.log. Hit CNTL-D to stop.
Some more advanced commands for the guru's:
ps -ef | grep inherit List all running Oracle Listeners
ps -ef | grep smon List all running Oracle Databases
ipcs | grep oracle Semaphores and shared memory segments belonging to oracle Remove with ipcrm, but be carefull!!!
ls -l . | awk '{total += $5}; END {print total}' Prints the total size (in bytes) of all files in the current directory
ls -lR . | awk '{total += $5}; END {print total/1024/1024 " Meg"}' Prints the total size of files in the current directory and subdirectories below
ls -lR | awk '{print $5 "\t" $9}' | sort -n | tail Find the largest files in dir and subdirecotry.
System Admin commands:
Function: Sun: Sequent: HP-UX: AIX: SCO:
System Config: /usr/sbin/psrinfo -v showcfg -s ? ? ?
Admin menu: admintool menu ? smit sysadmsh
Mount CD-Rom: ? ? ? ? ?
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Where can I get more info about Unix and Unix vendors?
General Reference FAQ Unix Gurus
SUN Vendor FAQ
HP Vendor FAQ
AIX Vendor FAQ
Sequent Vendor
Digital Vendor FAQ
SCO Vendor FAQ
NCR Vendor
SGI Vendor FAQ
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1 comment:
Nice article and thanks for sharing the information about the SQl and the extension of this language is plsql and tlsql.
SQL Queries Interview Questions and Answers
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