Part-1
Guide to Advanced Linux Command Mastery
learning some routine Linux commands, which are especially valuable for Linux newbies. But now that you have mastered the basics, let’s move on to some more sophisticated commands that you will find extremely useful.In this four-part series, you will learn some not-so-well-known tricks about various routine commands as well as variations in usage that make them more useful. As the series progresses, you will learn successively difficult commands to master.
Note that these commands may differ based on the specific version of Linux you use or which specific kernel is compiled, but if so, probably only slightly.
Painless Changes to Owner, Group, and Permissions
In Sheryl's article you learned how to use chown and chgrp commands to change ownership and group of the files. Say you have several files like this:# ls -ltotal 8-rw-r--r-- 1 ananda users 70 Aug 4 04:02 file1-rwxr-xr-x 1 oracle dba 132 Aug 4 04:02 file2-rwxr-xr-x 1 oracle dba 132 Aug 4 04:02 file3-rwxr-xr-x 1 oracle dba 132 Aug 4 04:02 file4-rwxr-xr-x 1 oracle dba 132 Aug 4 04:02 file5-rwxr-xr-x 1 oracle dba 132 Aug 4 04:02 file6and you need to change the permissions of all the files to match those of file1. Sure, you could issue chmod 644 * to make that change—but what if you are writing a script to do that, and you don’t know the permissions beforehand? Or, perhaps you are making several permission changes and based on many different files and you find it infeasible to go though the permissions of each of those and modify accordingly. A better approach is to make the permissions similar to those of another file. This command makes the permissions of file2 the same as file1:
chmod --reference file1 file2 Now if you check: # ls -l file[12]total 8-rw-r--r-- 1 ananda users 70 Aug 4 04:02 file1-rw-r--r-- 1 oracle dba 132 Aug 4 04:02 file2The file2 permissions were changed exactly as in file1. You didn’t need to get the permissions of file1 first. You can also use the same trick in group membership in files. To make the group of file2 the same as file1, you would issue:
# chgrp --reference file1 file2# ls -l file[12]-rw-r--r-- 1 ananda users 70 Aug 4 04:02 file1-rw-r--r-- 1 oracle users 132 Aug 4 04:02 file2Of course, what works for changing groups will work for owner as well. Here is how you can use the same trick for an ownership change. If permissions are like this: # ls -l file[12] -rw-r--r-- 1 ananda users 70 Aug 4 04:02 file1-rw-r--r-- 1 oracle dba 132 Aug 4 04:02 file2You can change the ownership like this: # chown --reference file1 file2# ls -l file[12] -rw-r--r-- 1 ananda users 70 Aug 4 04:02 file1-rw-r--r-- 1 ananda users 132 Aug 4 04:02 file2Note that the group as well as the owner have changed. Tip for Oracle Users
This is a trick you can use to change ownership and permissions of Oracle executables in a directory based on some reference executable. This proves especially useful in migrations where you can (and probably should) install as a different user and later move them to your regular Oracle software owner.More on Files
The ls command, with its many arguments, provides some very useful information on files. A different and less well known command – stat – offers even more useful information.Here is how you can use it on the executable “oracle”, found under $ORACLE_HOME/bin.
# cd $ORACLE_HOME/bin# stat oracle File: `oracle' Size: 93300148 Blocks: 182424 IO Block: 4096 Regular FileDevice: 343h/835d Inode: 12009652 Links: 1 Access: (6751/-rwsr-s--x) Uid: ( 500/ oracle) Gid: ( 500/ dba)Access: 2006-08-04 04:30:52.000000000 -0400Modify: 2005-11-02 11:49:47.000000000 -0500Change: 2005-11-02 11:55:24.000000000 -0500Note the information you got from this command: In addition to the usual filesize (which you can get from ls -l anyway), you got the number of blocks this file occupies. The typical Linux block size is 512 bytes, so a file of 93,300,148 bytes would occupy (93300148/512=) 182226.85 blocks. Since blocks are used in full, this file uses some whole number of blocks. Instead of making a guess, you can just get the exact blocks. You also get from the output above the GID and UID of the ownership of the file and the octal representation of the permissions (6751). If you want to reinstate it back to the same permissions it has now, you could use chmod 6751 oracle instead of explicitly spelling out the permissions.
The most useful part of the above output is the file access timestamp information. It shows you that the file was accessed on 2006-08-04 04:30:52 (as shown next to “Access:”), or August 4, 2006 at 4:30:52 AM. This is when someone started to use the database. The file was modified on 2005-11-02 11:49:47 (as shown next to Modify:). Finally, the timestamp next to “Change:” shows when the status of the file was changed.
-f, a modifier to the stat command, shows the information on the filesystem instead of the file:
# stat -f oracle File: "oracle" ID: 0 Namelen: 255 Type: ext2/ext3Blocks: Total: 24033242 Free: 15419301 Available: 14198462 Size: 4096Inodes: Total: 12222464 Free: 12093976 Another option, -t, gives exactly the same information but on one line: # stat -t oracle oracle 93300148 182424 8de9 500 500 343 12009652 1 0 0 1154682061 1130950187 1130950524 4096This is very useful in shell scripts where a simple cut command can be used to extract the values for further processing. Tip for Oracle Users
When you relink Oracle (often done during patch installations), it moves the existing executables to a different name before creating the new one. For instance, you could relink all the utilities byrelink utilities
It recompiles, among other things, the sqlplus executable. It moves the exiting executable sqlplus to sqlplusO. If the recompilation fails for some reason, the relink process renames sqlplusO to sqlplus and the changes are undone. Similarly, if you discover a functionality problem after applying a patch, you can quickly undo the patch by renaming the file yourself.
Here is how you can use stat on these files:
# stat sqlplus* File: 'sqlplus' Size: 9865 Blocks: 26 IO Block: 4096 Regular FileDevice: 343h/835d Inode: 9126079 Links: 1 Access: (0751/-rwxr-x--x) Uid: ( 500/ oracle) Gid: ( 500/ dba)Access: 2006-08-04 05:15:18.000000000 -0400Modify: 2006-08-04 05:15:18.000000000 -0400Change: 2006-08-04 05:15:18.000000000 -0400 File: 'sqlplusO' Size: 8851 Blocks: 24 IO Block: 4096 Regular FileDevice: 343h/835d Inode: 9125991 Links: 1 Access: (0751/-rwxr-x--x) Uid: ( 500/ oracle) Gid: ( 500/ dba)Access: 2006-08-04 05:13:57.000000000 -0400Modify: 2005-11-02 11:50:46.000000000 -0500Change: 2005-11-02 11:55:24.000000000 -0500It shows sqlplusO was modified on November 11, 2005, while sqlplus was modified on August 4, 2006, which also corresponds to the status change time of sqlplusO . It indicates that the original version of sqlplus was in effect from Nov 11, 2005 to Aug 4, 2006. If you want to diagnose some functionality issues, this is a great place to start. In addition to the file changes, as you know the permission's change time, you can correlate it with any perceived functionality issues. Another important output is size of the file, which is different—9865 bytes for sqlplus as opposed to 8851 for sqlplusO—indicating that the versions are not mere recompiles; they actually changed with additional libraries (perhaps). This also indicates a potential cause of some problems.
File Types
When you see a file, how do you know what type of file it is? The command file tells you that. For instance:# file alert_DBA102.logalert_DBA102.log: ASCII textThe file alert_DBA102.log is an ASCII text file. Let’s see some more examples: # file initTESTAUX.ora.ZinitTESTAUX.ora.Z: compress'd data 16 bitsThis tells you that the file is a compressed file, but how do you know the type of the file was compressed? One option is to uncompress it and run file against it; but that would make it virtually impossible. A cleaner option is to use the parameter -z: # file -z initTESTAUX.ora.ZinitTESTAUX.ora.Z: ASCII text (compress'd data 16 bits)Another quirk is the presence of symbolic links: # file spfile+ASM.ora.ORIGINAL spfile+ASM.ora.ORIGINAL: symbolic link to /u02/app/oracle/admin/DBA102/pfile/spfile+ASM.ora.ORIGINALThis is useful; but what type of file is that is being pointed to? Instead of running file again, you can use the option -l: # file -L spfile+ASM.ora.ORIGINALspfile+ASM.ora.ORIGINAL: dataThis clearly shows that the file is a data file. Note that the spfile is a binary one, as opposed to init.ora; so the file shows up as data file. Tip for Oracle Users
Suppose you are looking for a trace file in the user dump destination directory but are unsure if the file is located on another directory and merely exists here as a symbolic link, or if someone has compressed the file (or even renamed it). There is one thing you know: it’s definitely an ascii file. Here is what you can do:file -Lz * | grep ASCII | cut -d":" -f1 | xargs ls -ltrThis command checks the ASCII files, even if they are compressed, and lists them in chronological order. Comparing Files
How do you find out if two files—file1 and file2—are identical? There are several ways and each approach has its own appeal.diff. The simplest command is diff, which shows the difference between two files. Here are the contents of two files:
# cat file1In file1 onlyIn file1 and file2# cat file2In file1 and file2In file2 onlyIf you use the diff command, you will be able to see the difference between the files as shown below: # diff file1 file21d0< In file1 only2a2> In file2 only#In the output, a "<" in the first column indicates that the line exists on the file mentioned first,—that is, file1. A ">" in that place indicates that the line exists on the second file (file2). The characters 1d0 in the first line of the output shows what must be done in sed to operate on the file file1 to make it same as file2. Another option, -y, shows the same output, but side by side:
# diff -y file1 file2 -W 120In file1 only <In file1 and file2 In file1 and file2 > In file2 only If you just want to just know if the files differ, not necessarily how, you can use the -q option.
# diff -q file3 file4# diff -q file3 file2Files file3 and file2 differFiles file3 and file4 are the same so there is no output; in the other case, the fact that the files differ is reported. If you are writing a shell script, it might be useful to produce the output in such a manner that it can be parsed. The -u option does that:
# diff -u file1 file2 --- file1 2006-08-04 08:29:37.000000000 -0400+++ file2 2006-08-04 08:29:42.000000000 -0400@@ -1,2 +1,2 @@-In file1 onlyIn file1 and file2+In file2 onlyThe output shows contents of both files but suppresses duplicates, the + and - signs in the first column indicates the lines in the files. No character in the first column indicates presence in both files. The command considers whitespace into consideration. If you want to ignore whitespace, use the -b option. Use the -B option to ignore blank lines. Finally, use -i to ignore case.
The diff command can also be applied to directories. The command
diff dir1 dir2shows the files present in either directories; whether files are present on one of the directories or both. If it finds a subdirectory in the same name, it does not go down to see if any individual files differ. Here is an example: # diff DBA102 PROPRD Common subdirectories: DBA102/adump and PROPRD/adumpOnly in DBA102: afiedt.bufOnly in PROPRD: archiveOnly in PROPRD: BACKUPOnly in PROPRD: BACKUP1Only in PROPRD: BACKUP2Only in PROPRD: BACKUP3Only in PROPRD: BACKUP4Only in PROPRD: BACKUP5Only in PROPRD: BACKUP6Only in PROPRD: BACKUP7Only in PROPRD: BACKUP8Only in PROPRD: BACKUP9Common subdirectories: DBA102/bdump and PROPRD/bdumpCommon subdirectories: DBA102/cdump and PROPRD/cdumpOnly in PROPRD: CreateDBCatalog.logOnly in PROPRD: CreateDBCatalog.sqlOnly in PROPRD: CreateDBFiles.logOnly in PROPRD: CreateDBFiles.sqlOnly in PROPRD: CreateDB.logOnly in PROPRD: CreateDB.sqlOnly in DBA102: dpdumpOnly in PROPRD: emRepository.sqlOnly in PROPRD: init.oraOnly in PROPRD: JServer.sqlOnly in PROPRD: logOnly in DBA102: oradataOnly in DBA102: pfileOnly in PROPRD: postDBCreation.sqlOnly in PROPRD: RMANTEST.shOnly in PROPRD: RMANTEST.sqlCommon subdirectories: DBA102/scripts and PROPRD/scriptsOnly in PROPRD: sqlPlusHelp.logCommon subdirectories: DBA102/udump and PROPRD/udumpNote that the common subdirectories are simply reported as such but no comparison is made. If you want to drill down even further and compare files under those subdirectories, you should use the following command: diff -r dir1 dir2This command recursively goes into each subdirectory to compare the files and reports the difference between the files of the same names. Tip for Oracle Users
One common use of diff is to differentiate between different init.ora files. As a best practice, I always copy the file to a new name—e.g. initDBA102.ora to initDBA102.080306.ora (to indicate August 3,2006)—before making a change. A simple diff between all versions of the file tells quickly what changed and when.This is a pretty powerful command to manage your Oracle home. As a best practice, I never update an Oracle Home when applying patches. For instance, suppose the current Oracle version is 10.2.0.1. The ORACLE_HOME could be /u01/app/oracle/product/10.2/db1. When the time comes to patch it to 10.2.0.2, I don’t patch this Oracle Home. Instead, I start a fresh installation on /u01/app/oracle/product/10.2/db2 and then patch that home. Once it’s ready, I use the following:
# sqlplus / as sysdbaSQL> shutdown immediateSQL> exit# export ORACLE_HOME=/u01/app/oracle/product/10.2/db2# export PATH=$ORACLE_HOME/bin:$PATH# sqlplus / as sysdbaSQL> @$ORACLE_HOME/rdbms/admin/catalog...and so on. The purpose of this approach is that the original Oracle Home is not disturbed and I can easily fall back in case of problems. This also means the database is down and up again, pretty much immediately. If I installed the patch directly on the Oracle Home, I would have had to shut the database for a long time—for the entire duration of the patch application. In addition, if the patch application had failed due to any reason, I would not have a clean Oracle Home.
Now that I have several Oracle Homes, how can I see what changed? It’s really simple; I can use:
diff -r /u01/app/oracle/product/10.2/db1 /u01/app/oracle/product/10.2/db2 | grep -v CommonThis tells me the differences between the two Oracle Homes and the differences between the files of the same name. Some important files like tnsnames.ora, listener.ora, and sqlnet.ora should not show wide differences, but if they do, then I need to understand why. cmp. The command cmp is similar to diff:
# cmp file1 file2 file1 file2 differ: byte 10, line 1The output comes back as the first sign of difference. You can use this to identify where the files might be different. Like diff, cmp has a lot of options, the most important being the -s option, that merely returns a code: - 0, if the files are identical
- 1, if they differ
- Some other non-zero number, if the comparison couldn’t be made
# cmp -s file3 file4# echo $?0The special variable $? indicates the return code from the last executed command. In this case it’s 0, meaning the files file1 and file2 are identical. # cmp -s file1 file2# echo $?1means file1 and file2 are not the same. This property of cmp can prove very useful in shell scripting where you merely want to check if two files differ in any way, but not necessarily check what the difference is. Another important use of this command is to compare binary files, where diff may not be reliable.
Tip for Oracle Users
Recall from a previous tip that when you relink Oracle executables, the older version is kept prior to being overwritten. So, when you relink, the executable sqlplus is renamed to “sqlplusO” and the newly compiled sqlplus is placed in the $ORACLE_HOME/bin. So how do you ensure that the sqlplus that was just created is any different? Just use:# cmp sqlplus sqlplusOsqlplus sqlplusO differ: byte 657, line 7If you check the size: # ls -l sqlplus*-rwxr-x--x 1 oracle dba 8851 Aug 4 05:15 sqlplus-rwxr-x--x 1 oracle dba 8851 Nov 2 2005 sqlplusOEven though the size is the same in both cases, cmp proved that the two programs differ. comm. The command comm is similar to the others but the output comes in three columns, separated by tabs. Here is an example:
# comm file1 file2 In file1 and file2In file1 onlyIn file1 and file2 In file2 onlySummary of Commands in This Installment
|
# comm -1 file1 file2In file1 and file2In file2 onlymd5sum. This command generates a 32-bit MD5 hash value of the files: # md5sum file1ef929460b3731851259137194fe5ac47 file1Two files with the same checksum can be considered identical. However, the usefulness of this command goes beyond just comparing files. It can also provide a mechanism to guarantee the integrity of the files. Suppose you have two important files—file1 and file2—that you need to protect. You can use the --check option check to confirm the files haven't changed. First, create a checksum file for both these important files and keep it safe:
# md5sum file1 file2 > f1f2 Later, when you want to verify that the files are still untouched: # md5sum --check f1f2 file1: OKfile2: OKThis shows clearly that the files have not been modified. Now change one file and check the MD5: # cp file2 file1# md5sum --check f1f2file1: FAILEDfile2: OKmd5sum: WARNING: 1 of 2 computed checksums did NOT matchThe output clearly shows that file1 has been modified. Tip for Oracle Users
md5sum is an extremely powerful command for security implementations. Some of the configuration files you manage, such as listener.ora, tnsnames.ora, and init.ora, are extremely critical in a successful Oracle infrastructure and any modification may result in downtime. These are typically a part of your change control process. Instead of just relying on someone’s word that these files have not changed, enforce it using MD5 checksum. Create a checksum file and whenever you make a planned change, recreate this file. As a part of your compliance, check this file using the md5sum command. If someone inadvertently updated one of these key files, you would immediately catch the change.In the same line, you can also create MD5 checksums for all executables in $ORACLE_HOME/bin and compare them from time to time for unauthorized modifications.
Conclusion
Thus far you have learned only some of the Linux commands you will find useful for performing your job effectively. In the next installment, I will describe some more sophisticated but useful commands, such as strace, whereis, renice, skill, and more.Part-2
Guide to Advanced Linux Command Mastery, Part 2
by Arup Nanda
In Part 1 of the series, you learned some useful commands not so widely known and some of the often used commands but not-so-well-known parameters to do your job more efficiently. Continuing on the series, now you will learn some slightly more advanced Linux commands useful for Oracle users, whether developers or DBAs.
alias and unalias
Suppose you want to check the ORACLE_SID environment variable set in your shell. You will have to type:echo $ORACLE_HOMEAs a DBA or a developer, you frequently use this command and will quickly become tired of typing the entire 16 characters. Is there is a simpler way? There is: the alias command. With this approach you can create a short alias, such as "os", to represent the entire command:
alias os='echo $ORACLE_HOME'Now whenever you want to check the ORACLE_SID, you just type "os" (without the quotes) and Linux executes the aliased command. However, if you log out and log back in, the alias is gone and you have to enter the alias command again. To eliminate this step, all you have to do is to put the command in your shell's profile file. For bash, the file is .bash_profile (note the period before the file name, that's part of the file's name) in your home directory. For bourne and korn shells, it's .profile, and for c-shell, .chsrc.
You can create an alias in any name. For instance, I always create an alias for the command rm as rm -i, which makes the rm command interactive.
alias rm=’rm -i’Whenever I issue an rm command, Linux prompts me for confirmation, and unless I provide "y", it doesn't remove the file—thus I am protected form accidentally removing an important file. I use the same for mv (for moving the file to a new name), which prevents accidental overwriting of existing files, and cp (for copying the file). Here is a list of some very useful aliases I like to define:
alias bdump='cd $ORACLE_BASE/admin/$ORACLE_SID/bdump'alias l='ls -d .* --color=tty'alias ll='ls -l --color=tty'alias mv='mv -i'alias oh='cd $ORACLE_HOME'alias os='echo $ORACLE_SID'alias rm='rm -i'alias tns='cd $ORACLE_HOME/network/admin'To see what aliases have been defined in your shell, use alias without any parameters. However, there is a small problem. I have defined an alias, rm, that executes rm -i. This command will prompt for my confirmation every time I try to delete a file. But what if I want to remove a lot of files and am confident they can be deleted without my confirmation?
The solution is simple: To suppress the alias and use the command only, I will need to enter two single quotes:
$ ''rm *Note, these are two single quotes (') before the rm command, not two double quotes. This will suppress the alias rm. Another approach is to use a backslash (\): $ \rm *To remove an alias previously defined, just use the unalias command:$ unalias rmls
The humble ls command is frequently used but rarely to its full potential. Without any options, ls merely displays all files and directories in tabular format.$ lsadmin has mesg precompapex hs mgw racgassistants install network rdbms... output snipped ...To show them in a list, use the -1 (this is the number 1, not the letter "l") option.$ ls -1adminapexassistants... output snipped ...This option is useful in shell scripts where the files names need to be fed into another program or command for manipulation.You have most definitely used the -l (the letter "l", not the number "1") that displays all the attributes of the files and directories. Let's see it once again:
$ ls -l total 272drwxr-xr-x 3 oracle oinstall 4096 Sep 3 03:27 admindrwxr-x--- 7 oracle oinstall 4096 Sep 3 02:32 apexdrwxr-x--- 7 oracle oinstall 4096 Sep 3 02:29 assistantsThe first column shows the type of file and the permissions on it: "d" means directory, "-" means a regular file, "c" means a character device, "b" means a block device, "p" means named pipe, and "l" (that's a lowercase letter L, not I) means symbolic link.One very useful option is --color, which shows the files in many different colors based on the type of file. Here is an example screenshot:
Note that files file1 and file2 are regular files. link1 is a symbolic link, shown in red; dir1 is a directory, shown in yellow; and pipe1 is a named pipe, shown in different colors for easier identification.
In some distros, the ls command comes pre-installed with an alias (described in the previous section) as ls --color; so you can see the files in color when you type "ls". This approach may be undesirable, however, especially if you have an output like that above. You can change the colors, but a quicker way may be just to turn off the alias:
$ alias ls="''ls" Another useful option is the -F option, which appends a symbol after each file to show the type of the file - a "/" after directories, "@" after symbolic links, and "|" after named pipes.$ ls -Fdir1/ file1 file2 link1@ pipe1|If you have a subdirectory under a directory and you want to list only that directory, ls -l will show you the contents of the subdirectory as well. For instance, suppose the directory structure is like the following:/dir1+-->/subdir1+--> subfile1+--> subfile2The directory dir1 has a subdirectory subdir1 and two files: subfile1 and subfile2. If you just want to see the attributes of the directory dir1, you issue:$ ls -l dir1total 4drwxr-xr-x 2 oracle oinstall 4096 Oct 14 16:52 subdir1-rw-r--r-- 1 oracle oinstall 0 Oct 14 16:48 subfile1-rw-r--r-- 1 oracle oinstall 0 Oct 14 16:48 subfile2Note that the directory dir1 is not listed in the output. Rather, the contents of the directory are displayed. This is expected behavior when processing directories. To show the directory dir1 only, you will have to use the -d command.$ ls -dl dir1drwxr-xr-x 3 oracle oinstall 4096 Oct 14 16:52 dir1If you notice the output of the following ls -l output:-rwxr-x--x 1 oracle oinstall 10457761 Apr 6 2006 rmanO-rwxr-x--x 1 oracle oinstall 10457761 Sep 23 23:48 rman-rwsr-s--x 1 oracle oinstall 93300507 Apr 6 2006 oracleO-rwx------ 1 oracle oinstall 93300507 Sep 23 23:49 oracleYou will notice that the sizes of the files are shown in bytes. This may be easy in small files but when file sizes are pretty large, a long number may not be very easy to read. The option "-h" comes handy then, to display the size in a human readable form.$ ls -lh -rwxr-x--x 1 oracle oinstall 10M Apr 6 2006 rmanO-rwxr-x--x 1 oracle oinstall 10M Sep 23 23:48 rman-rwsr-s--x 1 oracle oinstall 89M Apr 6 2006 oracleO-rwx------ 1 oracle oinstall 89M Sep 23 23:49 oracleNote how the size has been shown in M (for megabytes), K (for kilobytes), and so on.$ ls -lrThe parameter -r shows the output in the reverse order. In this command, the files will be shown in the reverse alphabetical order.$ ls -lRThe -R operator makes the ls command execute recursively—that is, go under to the subdirectories and show those files too.What if you want to show the largest to the smallest files? This can be done with the -S parameter.
$ ls -lS total 308-rw-r----- 1 oracle oinstall 52903 Oct 11 18:31 sqlnet.log-rwxr-xr-x 1 oracle oinstall 9530 Apr 6 2006 root.shdrwxr-xr-x 2 oracle oinstall 8192 Oct 11 18:14 bindrwxr-x--- 3 oracle oinstall 8192 Sep 23 23:49 libxargs
Most Linux commands are about getting an output: a list of files, a list of strings, and so on. But what if you want to use some other command with the output of the previous one as a parameter? For example, the filels -l command to see the timestamp. The command xargs does exactly that. It allows you to execute some other commands on the output. Remember this syntax from Part 1: command shows the type of the file (executable, ascii text, and so on); you can manipulate the output to show only the filenames and now you want to pass these names to thefile -Lz * | grep ASCII | cut -d":" -f1 | xargs ls -ltrLet's dissect this command string. The first, file -Lz *, finds files that are symbolic links or compressed. It passes the output to the next command, grep ASCII, which searches for the string "ASCII" in them and produces the output similar to this:
alert_DBA102.log: ASCII English textalert_DBA102.log.Z: ASCII text (compress'd data 16 bits)dba102_asmb_12307.trc.Z: ASCII English text (compress'd data 16 bits)dba102_asmb_20653.trc.Z: ASCII English text (compress'd data 16 bits)Since we are interested in the file names only, we applied the next command, cut -d":" -f1, to show the first field only:
alert_DBA102.logalert_DBA102.log.Zdba102_asmb_12307.trc.Zdba102_asmb_20653.trc.ZNow, we want to use the ls -l command and pass the above list as parameters, one at a time. The xargsxargs ls -ltr, takes the output and executes the command ls -ltr against them, as if executing: command allowed you to to that. The last part, ls -ltr alert_DBA102.logls -ltr alert_DBA102.log.Zls -ltr dba102_asmb_12307.trc.Zls -ltr dba102_asmb_20653.trc.ZThus xargs is not useful by itself, but is quite powerful when combined with other commands.Here is another example, where we want to count the number of lines in those files:
$ file * | grep ASCII | cut -d":" -f1 | xargs wc -l 47853 alert_DBA102.log 19 dba102_cjq0_14493.trc 29053 dba102_mmnl_14497.trc 154 dba102_reco_14491.trc 43 dba102_rvwr_14518.trc 77122 total(Note: the above task can also be accomplished with the following command:)$ wc -l ‘file * | grep ASCII | cut -d":" -f1 | grep ASCII | cut -d":" -f1‘The xargs version is given to illustrate the concept. Linux has several ways to achieve the same task; use the one that suits your situation best.Using this approach you can quickly rename files in a directory.
$ ls | xargs -t -i mv {} {}.bakThe -i option tells xargs to replace {} with the name of each item. The -t option instructs xargs to print the command before executing it.Another very useful operation is when you want to open the files for editing using vi:
$ file * | grep ASCII | cut -d":" -f1 | xargs viThis command opens the files one by one using vi. When you want to search for many files and open them for editing, this comes in very handy. It also has several options. Perhaps the most useful is the -p option, which makes the operation interactive:
$ file * | grep ASCII | cut -d":" -f1 | xargs -p vivi alert_DBA102.log dba102_cjq0_14493.trc dba102_mmnl_14497.trc
dba102_reco_14491.trc dba102_rvwr_14518.trc ?...Here xarg asks you to confirm before running each command. If you press "y", it executes the command. You will find it immensely useful when you take some potentially damaging and irreversible operations on the file—such as removing or overwriting it.The -t option uses a verbose mode; it displays the command it is about to run, which is a very helpful option during debugging.
What if the output passed to the xargs is blank? Consider:
$ file * | grep SSSSSS | cut -d":" -f1 | xargs -t wc -lwc -l 0$Here searching for "SSSSSS" produces no match; so the input to xargs is all blanks, as shown in the second line (produced since we used the -t, or the verbose option). Although this may be useful, In some cases you may want to stop xargs if there is nothing to process; if so, you can use the -r option:
$ file * | grep SSSSSS | cut -d":" -f1 | xargs -t -r wc -l$The command exits if there is nothing to run.Suppose you want to remove the files using the rm command, which should be the argument to the xargsrm can accept a limited number of arguments. What if your argument list exceeds that limit? The -n option to xargs limits the number of arguments in a single command line. command. However,
Here is how you can limit only two arguments per command line: Even if five files are passed to xargs ls -ltr, only two files are passed to ls -ltr at a time.
$ file * | grep ASCII | cut -d":" -f1 | xargs -t -n2 ls -ltr ls -ltr alert_DBA102.log dba102_cjq0_14493.trc -rw-r----- 1 oracle dba 738 Aug 10 19:18 dba102_cjq0_14493.trc-rw-r--r-- 1 oracle dba 2410225 Aug 13 05:31 alert_DBA102.logls -ltr dba102_mmnl_14497.trc dba102_reco_14491.trc -rw-r----- 1 oracle dba 5386163 Aug 10 17:55 dba102_mmnl_14497.trc-rw-r----- 1 oracle dba 6808 Aug 13 05:21 dba102_reco_14491.trcls -ltr dba102_rvwr_14518.trc -rw-r----- 1 oracle dba 2087 Aug 10 04:30 dba102_rvwr_14518.trcUsing this approach you can quickly rename files in a directory. $ ls | xargs -t -i mv {} {}.bakThe -i option tells xargs to replace {} with the name of each item. rename
As you know, the mv command renames files. For example,$ mv oldname newnamerenames the file oldname to newname. However, what if you don't know the filenames yet? The rename command comes in really handy here.
rename .log .log.‘date +%F-%H:%M:%S‘ *replaces all files with the extension .log with .log.find
Among the most popular for Oracle users is the find command. By now you know about using find to find files on a given directory. Here is an example to find files starting with the word "file" in the current directory:$ find . -name "file*"./file2./file1./file3./file4However, what if you want to search for names like FILE1, FILE2, and so on? The -name "file*" will not match them. For a case-insensitive search, use the -iname option:$ find . -iname "file*"./file2./file1./file3./file4./FILE1./FILE2You can limit your search to a specific type of files only. For instance, the above command will get the files of all types: regular files, directories, symbolic links, and so on. To search for only regular files, you can use the -type f parameter.$ find . -name "orapw*" -type f ./orapw+ASM./orapwDBA102./orapwRMANTEST./orapwRMANDUP./orapwTESTAUXThe -type can take the modifiers f (for regular files), l (for symbolic links), d (directories), b (block devices), p (named pipes), c (character devices), s (sockets).A slight twist to the above command is to combine it with the file command you learned about in Part 1. The command file tells you what type of file it is. You can pass it as a post processor for the output from find command. The -exec parameter executes the command following the parameter. In this case, the command to execute after the find is file:
$ find . -name "*oraenv*" -type f -exec file {} \;./coraenv: Bourne shell script text executable./oraenv: Bourne shell script text executableThis is useful when you want to find out if the ASCII text file could be some type of shell script. If you substitute -exec with -ok, the command is executed but it asks for your confirmation first. Here's an example:
$ find . -name "sqlplus*" -ok {} \; < {} ... ./sqlplus > ? ySQL*Plus: Release 9.2.0.5.0 - Production on Sun Aug 6 11:28:15 2006Copyright (c) 1982, 2002, Oracle Corporation. All rights reserved.Enter user-name: / as sysdbaConnected to:Oracle9i Enterprise Edition Release 9.2.0.5.0 - 64bit ProductionWith the Partitioning, Real Application Clusters, OLAP and Oracle Data Mining optionsJServer Release 9.2.0.5.0 - ProductionSQL> exitDisconnected from Oracle9i Enterprise Edition Release 9.2.0.5.0 - 64bit ProductionWith the Partitioning, Real Application Clusters, OLAP and Oracle Data Mining optionsJServer Release 9.2.0.5.0 - Production< È* ... ./sqlplusO > ? n$Here we have asked the shell to find all programs starting with "sqlplus", and execute them. Note there is nothing between -ok and {}, so it will just execute the files it finds. It finds two files—sqlplus and sqlplusO—and asks in each case if you want to execute it. We answered "y" to the prompt against "sqlplus" and it executed. After exiting, it prompted the second file it found (sqlplusO) and for confirmation again again, to which we answered "n"—thus, it was not executed.
Tip for Oracle Users
Oracle produces many extraneous files: trace files, log files, dump files, and so on. Unless they are cleaned periodically, they can fill up the filesystem and bring the database to a halt.To ensure that doesn't happen, simply search for the files with extension "trc" and remove them if they are more than three days old. A simple command does the trick:
find . -name "*.trc" -ctime +3 -exec rm {} \;To forcibly remove them prior to the three-day limit, use the -f option. find . -name "*.trc" -ctime +3 -exec rm -f {} \;If you just want to list the files:find . -name "*.trc" -ctime +3 -exec ls -l {} \;m4
This command takes an input file and substitutes strings inside it with the parameters passed, similar to substituting for variables. For example, here is an input file:$ cat tempThe COLOR fox jumped over the TYPE fence.Were you to substitute the strings "COLOR" by "brown" and "TYPE" by "broken", you could use: $ m4 -DCOLOR=brown -DTYPE=broken tempThe brown fox jumped over the broken fence.Else, if you want to substitute "white" and "high" for the same: $ m4 -DCOLOR=white -DTYPE=high temp The white fox jumped over the high fence.whence and which
These commands are used to find out the where the executables mentioned are stored in the PATH of the user. When the executable is found in the path, they behave pretty much the same way and display the path: $ which sqlplus /u02/app/oracle/products/10.2.0.1/db1/bin/sqlplus$ whence sqlplus /u02/app/oracle/products/10.2.0.1/db1/bin/sqlplusThe output is identical. However, if the executable is not found in the path, the behavior is different. The which command produces an explicit message:$ which sqlplus1/usr/bin/which: no sqlplus1 in (/u02/app/oracle/products/10.2.0.1/db1/bin:/usr
/kerberos/bin:/usr/local/bin:/bin:/usr/bin:/usr/X11R6/bin)whereas the whence command produces no message:$ whence sqlplus1]and returns to shell prompt. This is useful in cases where the executable is not found in the path (instead of displaying the message): $ whence invalid_command$ which invalid_commandwhich: no invalid_command in (/usr/kerberos/sbin:/usr/kerberos/bin:/bin:/sbin:
/usr/bin:/usr/sbin:/usr/local/bin:/usr/local/sbin: /usr/bin/X11:/usr/X11R6/bin:/root/bin) When whence does not find an executable in the path, it returns without any message but the return code is not zero. This fact can be exploited in shell scripts; for example: RC=‘whence myexec‘If [ $RC -ne "0" ]; then echo "myexec is not in the $PATH"fiA very useful option to which is the -i option, which displays the alias as well as the executable, if present. For example, you saw the use of the alias at the beginning of this article. The rm command is actually an alias in my shell, and there is an rm command elsewhere in the system as well. $ which ls/bin/ls $ which -i lsalias ls='ls --color=tty' /bin/lsThe default behavior of which is to show the first occurrence of the executable in the path. If the executable exists in different directories in the path, the subsequent occurrences are ignored. You can see all the occurrences of the executable via the -a option. $ which java /usr/bin/java $ which -a java/usr/bin/java/home/oracle/oracle/product/11.1/db_1/jdk/jre/bin/javatop
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, 0.18shows 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. The second line:
151 processes: 147 sleeping, 4 running, 0 zombie, 0 stoppedshows 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_cSwap: 2041192k av, 122476k used, 1918716k free 591776k cachedshow 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 |
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_PRODB2Now 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 13554This 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.programfrom v$session s, v$process pwhere spid = 16143and 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 1After 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 16514This 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 oracleYou can use a user, a PID, a command or terminal id as argument. The following stops all rman commands.$ skill -STOP rmanAs 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 oracleall 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 oracleThe 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 oracleNow, 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 oracleNote 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. 
