UNIX / Linux Command To Check Existing Groups and Users

Find out if user exists in /etc/passwd file

/etc/passwd file stores essential information required during login. All you have to do is search this file for user name using following syntax:
$ egrep -i "^username" /etc/passwd
For, example find out if vivek user exists or not, enter:
$ egrep -i "^vivek" /etc/passwd
Sample output:

vivek:x:1000:1000:Vivek Gite,,,,:/home/vivek:/bin/bash

A quick shell script code:

#!/bin/bash
# init
USERID="$1"
#....
/bin/egrep  -i "^${USERID}" /etc/passwd
if [ $? -eq 0 ]; then
   echo "User $USERID exists in /etc/passwd"
else
   echo "User $USERID does not exists in /etc/passwd"
fi
# ....

Normally, exit status is 0 returned if user accounts (lines) are found and 1 otherwise.

Find out if group exists in /etc/group file

/etc/group is an text file which defines the groups to which users belong under Linux and UNIX operating system. Again, you have to search /etc/group file using following syntax:
$ egrep -i "^groupname" /etc/group
For, example find out if vivek group exists or not, enter:
$ egrep -i "^vivek" /etc/group

id command

id is another command to display user / group information for any USERNAME, or the current user. To find out more about user called, tom, enter:
$ id tom
Sample output

id: tom: No such user

To find out ftpuser group, enter:
$ id -g ftpuser
Sample output:

id: ftpuser: No such user

id command exit status is 0 returned if user accounts (lines) are found and 1 otherwise. A sample shell script using id command:

#!/bin/bash
USERID="$1"
/bin/id $USERID 2>/dev/null
[ $? -eq 0 ] && echo "User found" || echo "User not found"
 
/bin/id -g $USERID 2>/dev/null
[ $? -eq 0 ] && echo "Group found" || echo "Group not found"
 

reference:

http://www.cyberciti.biz/faq/linux-check-existing-groups-users/

Oracle10g/Linux Errors and Problems

Here is a list of common Oracle10g installation problems and other issues.

Note that most of the issues are due to not following the installation procedure correctly. And some errors are due to not using an Oracle supported Linux OS.

The Installation log file can be found in $ORACLE_BASE/oraInventory/logs.
The Database Creation log file can be found in $ORACLE_BASE/admin/$ORACLE_SID/create.

Checking monitor: must be configured to display at least 256 colors    Failed <<<<   >>> Could not execute auto check for display colors using command /usr/X11R6/bin/xdpyinfo. Check if the DISPLAY variable is set.    Some optional pre-requisite checks have failed (see above). Continue? (y/n) [n]

I ignored this error message on my system and said "Yes" to continue. But if you want to fix it and get rid of this error message, ensure the following RPMS are installed:

rpm -q XFree86 xf86tools cabextract libpng libjpeg XFree86-Mesa

Example for installing these packages on SLES-9 (packages can be found on the 2nd CD):

su - root
rpm -Uvh XFree86-4.3.99.902-43.22.i586.rpm \
         XFree86-Mesa-4.3.99.902-43.22.i586.rpm \
         xf86tools-0.1-955.5.i586.rpm \
         cabextract-1.0-17.1.i586.rpm \
         libpng-1.2.5-182.4.i586.rpm \
         libjpeg-6.2.0-731.1.i586.rpm

Enterprise manager configuration failed due to the following error -    Failed to allocate port(s) int the specified range for the following process(es):   JMS [5540-5559], RMI [5520-5539], Database Control [5500-5519], EM agent [1830-1849]

The problem is that ports listed in /etc/services are discounted. The workaround is to specify the ports manually, see emca -h. Use the following options and use the port ranges as specified in the above error message:

emca -RMI_PORT  -JMS_PORT  -AGENT_PORT  -DBCONSOLE_HTTP_PORT 

ORA-01034: ORACLE not available   ORA-27101: shared memory realm does not exist   Linux Error: 2: No such file or directory
  or
  ORA-01034: ORACLE not available

First check if ORACLE_SID is set correctly. If ORACLE_SID is set correctly, then you probably have a trailing slash "/" on the ORACLE_HOME environment variable. Remove it and try again to connect to sys (e.g from ORACLE_HOME=/u01/app/oracle/product/10.1.0/db_1/ to ORACLE_HOME=/u01/app/oracle/product/10.1.0/db_1).

ORA-01034: ORACLE not available   ORA-27121: unable to determine size of shared memory segment   Linux Error: 13: Permission denied

Make sure the SUID/SGID bits are set for $ORACLE_HOME/bin/oracle:

ls -l $ORACLE_HOME/bin/oracle
-rwsr-s--x  1 oracle oinstall 72524978 Dec 26 13:12 /u01/app/oracle/OraHome_1/bin/oracle

ORA-00988 missing or invalid password(s).

During the Oracle10g installation you probably provided a password for the Oracle database accounts that started with a digit number. Ignore this error message and change the password when you are done with the Oracle10g installation.

X11 connection rejected because of wrong authentication.   X connection to localhost:10.0 broken (explicit kill or server shutdown).

To rectify this problem, try to login to the remote Oracle server again by using the "X11 forward" feature of ssh. Execute the following command from your local desktop:

$ ssh -X oracle@oracle_remote_server_name

Now when you try to run any GUI tool on the remote server, it will automatically be relinked to your local desktop. If this is not working, verify that the ForwardX11 setting is not set to "no" in /etc/ssh/ssh_config on your remote server:

su - root
grep ForwardX11 /etc/ssh/ssh_config
#   ForwardX11 no
ForwardX11Trusted yes

If you are using telnet, however, you will have to set DISPLAY manually, see my other article Starting runInstaller for more information.

./runInstaller: line 67:  6275 Segmentation fault      $CMDDIR/install/runInstaller -formCluster $*

This error can come up if your system does not have a swap space.

Preparing to launch Oracle Universal Installer from /tmp/OraInstall2005-03-13_03-53-51PM.   Please wait .../tmp/OraInstall2005-03-13_03-53-51PM/oui/lib/linux/libclntsh.so.9.0  bad CRC c0265abb  (should be f138c206)    Error in writing to directory /tmp/OraInstall2005-03-13_03-53-51PM. Please ensure that this directory is writable and   has atleast 60 MB of disk space. Installation cannot continue. 

Sometimes I'm getting this error message. Simply try again.

Recovery Manager rman hangs

You are probably running the wrong rman binary which belongs to the XFree86-devel RPM:

$ which rman
/usr/X11R6/bin/rman

source and reference 

http://www.puschitz.com/InstallingOracle10gOnSUSE.shtml#TipsAndHintsForOracle10gOnLinux

Operations Behind BACKUP ... PLUS ARCHIVELOG Command.

Backing Up Logs with BACKUP ... PLUS ARCHIVELOG
You can add archived redo logs to a backup of other files by using the BACKUP ...PLUS ARCHIVELOG clause. Adding BACKUP ... PLUS ARCHIVELOG causes RMAN to do the following:
1. Runs the ALTER SYSTEM ARCHIVE LOG CURRENT command.
2. Runs BACKUP ARCHIVELOG ALL. Note that if backup optimization is enabled, then RMAN skips logs that it has already backed up to the specified device.
3. Backs up the rest of the files specified in BACKUP command.
4. Runs the ALTER SYSTEM ARCHIVE LOG CURRENT command.
5. Backs up any remaining archived logs generated during the backup.

This guarantees that datafile backups taken during the command are recoverable to a consistent state.
To back up archived redo logs with BACKUP ... PLUS ARCHIVELOG:
After starting RMAN, run the BACKUP ... PLUS ARCHIVELOG command at the RMAN prompt . This example backs up the database and all archived logs:
BACKUP DEVICE TYPE sbt DATABASE PLUS ARCHIVELOG;
note: If backup optimization is enabled, then RMAN skips backups of archived logs that have already been backed up to the specified device.

UNIX system, small sampling of commands on various topics.

1 Communication

cu	Connect to UNIX system.
ftp	File transfer protocol.
login	Sign on to UNIX.
mailx	Read or send mail.
rlogin	Sign on to remote UNIX.
talk	Write to other terminals.
telnet	Connect to another system.
vacation	Respond to mail automatically.
write	Write to other terminals.

2 Comparisons

cmp	Compare two files.
comm	Compare items in files.
diff	Compare two files.
diff3	Compare three files.
dircmp	Compare directories.
sdiff	Compare two files, side by side.

3 File Management

cat	Join files or display them.
cd	Change directory.
chmod	Change access modes on files.
cp	Copy files.
csplit	Break files at specific locations.
file	Determine a file's type.
head	Show the first few lines of a file.
install	Set up system files.
ln	Create filename aliases.
ls	List files or directories.
mkdir	Create a directory.
more	Display files by screenful.
mv	Move or rename files or directories.
pwd	Print your working directory.
rcp	Copy files to remote system.
rm	Remove files.
rmdir	Remove directories.
split	Split files evenly.
tail	Show the last few lines of a file.
wc	Count lines, words, and characters.

4 Miscellaneous

banner	Make posters from words.
bc	Precision calculator.
cal	Display calendar.
calendar	Check for reminders.
clear	Clear the screen.
kill	Terminate a running command.
man	Get information on a command.
nice	Reduce a job's priority.
nohup	Preserve a job after logging out.
passwd	Set password.
script	Produce a transcript of your login session.
spell	Report misspelled words.
su	Become a superuser.

5 Printing

cancel	Cancel a printer request.
lp	Send to the printer.
lpstat	Get printer status.
pr	Format and paginate for printing.

6 Programming

cb	C source code "beautifier."
cc	C compiler.
cflow	C function flowchart.
ctags	C function references.
ctrace	C debugger.
cxref	C cross-references.
lint	C debugger.
ld	Link editor.
lex	Lexical analyzer.
make	Execute commands in a specified order.
od	Dump input in various formats.
sdb	Symbolic debugger.
strip	Remove data from an object file.
truss	Trace signals and system calls.
yacc	Compiler used with lex.

7 Searching

egrep	Extended version of grep.
fgrep	Search files for literal words.
find	Search the system for filenames.
grep	Search files for text patterns.
strings	Search binary files for text patterns.

8 Shell Programming

echo	Repeat input on the output.
expr	Perform arithmetic and comparisons.
line	Read a line of input.
sleep	Pause during processing.
test	Test a condition.

9 Storage

compress	Compress files to free up space.
cpio	Copy archives in or out.
pack	Pack files to free up space.
pcat	Display contents of packed files.
tar	Tape archiver.
uncompress	Expand compressed (.Z) files.
unpack	Expand packed (.z) files.
zcat	Display contents of compressed files.

10 System Status

at	Execute commands later.
chgrp	Change file group.
chown	Change file owner.
crontab	Automate commands.
date	Display or set date.
df	Show free disk space.
du	Show disk usage.
env	Show environment variables.
finger	Point out information about users.
ps	Show processes.
ruptime	Show loads on working systems.
shutdown	Revert to single-user mode.
stty	Set or display terminal settings.
who	Show who is logged on.

11 Text Processing

cut	Select columns for display.
ex	Line-editor underlying vi.
fmt	Produce roughly uniform line lengths.
fold	Produce exactly uniform line lengths.
join	Merge different columns into a database.
nawk	New version of awk (pattern-matching language for database files).
paste	Merge columns or switch order.
sed	Noninteractive text editor.
sort	Sort or merge files.
tr	Translate (redefine) characters.
uniq	Find repeated or unique lines in a file.
vi	Visual text editor.
xargs	Process many arguments in manageable portions.

12 Troff

All but deroff are in the compatibility packages.

deroff	Remove troff codes.
eqn	Preprocessor for equations.
nroff	Formatter for terminal display.
pic	Preprocessor for line graphics.
tbl	Preprocessor for tables.
troff	Formatter for typesetting.

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