openssl: error while loading shared libraries: libssl.so.1.1: cannot open shared object file: No such file or directory

 [root@ISTELAR-DR ~]# openssl -version
openssl: error while loading shared libraries: libssl.so.1.1: cannot open shared object file: No such file or directory
[root@ISTELAR-DR ~]# ll /usr/lib64/libssl*
-rwxr-xr-x 1 root root 339232 Oct  9  2018 /usr/lib64/libssl3.so
lrwxrwxrwx 1 root root     16 Sep 16  2019 /usr/lib64/libssl.so -> libssl.so.1.0.1e
-rwxr-xr-x 1 root root 324456 Mar  9  2016 /usr/lib64/libssl.so.0.9.8e
lrwxrwxrwx 1 root root     16 Sep 16  2019 /usr/lib64/libssl.so.10 -> libssl.so.1.0.1e
-rwxr-xr-x 1 root root 446344 Aug 13  2019 /usr/lib64/libssl.so.1.0.1e
lrwxrwxrwx 1 root root     16 Apr 23  2018 /usr/lib64/libssl.so.6 -> libssl.so.0.9.8e
[root@ISTELAR-DR ~]# echo $LD_LIBRARY_PATH

[root@ISTELAR-DR ~]# ll /usr/local/liblibssl*
lib/     lib64/   libexec/
[root@ISTELAR-DR ~]# ll /usr/local/lib64/libssl*
-rw-r--r-- 1 root root 1024502 May 31 19:01 /usr/local/lib64/libssl.a
lrwxrwxrwx 1 root root      13 May 31 19:01 /usr/local/lib64/libssl.so -> libssl.so.1.1
-rwxr-xr-x 1 root root  684412 May 31 19:01 /usr/local/lib64/libssl.so.1.1
-rwxr-xr-x 1 root root  766712 May 31 18:52 /usr/local/lib64/libssl.so.3
[root@ISTELAR-DR ~]# export LD_LIBRARY_PATH = /usr/local/lib64:$LD_LIBRARY_PATH
-bash: export: `=': not a valid identifier
-bash: export: `/usr/local/lib64:': not a valid identifier
[root@ISTELAR-DR ~]# export LD_LIBRARY_PATH=/usr/local/lib64:$LD_LIBRARY_PATH
[root@ISTELAR-DR ~]# ln -s /usr/local/lib64/libssl.so.1.1 /usr/lib64/libssl.so.1.1
[root@ISTELAR-DR ~]# ln -s /usr/local/lib64/libcrypto.so.1.1 /usr/lib64/libcrypto.so.1.1
[root@ISTELAR-DR ~]# openssl -version
Invalid command '-version'; type "help" for a list.
[root@ISTELAR-DR ~]# openssl version
OpenSSL 1.1.1o  3 May 2022
[root@ISTELAR-DR ~]#
[root@ISTELAR-DR ~]#
[root@ISTELAR-DR ~]#

RHCE 7 Exam Practice with Solution Part-2 (EX 300)

7) Link Aggregation:-

--->configure your serverX and DesktopX which watches for link changes and selects on active port for data transfors.
--->ServerX should have the address as 192.168.0.100/255.255.255.0
--->DesktopX should have the address as 192.168.0.100/255.255.255.0

Solution:

[root@server7 ~]#nmcli connection show
[root@server7 ~]#nmcli connection add con-name team0 type team ifname team0 config '{"runner":{"name":"activebackup"}}'
[root@server7 ~]#teamdctl team0 state [Default is round robin here we are going to setup active backup]
[root@server7 ~]#nmcli connection modify team0 ipv4.addresses 192.168.0.100/24 ipv4.method static
[root@server7 ~]#nmcli connection down team0 ;nmcli connection up team0
[root@server7 ~]#nmcli connection add con-name team0-port1 type team-slave ifname eno33554992 master team0
[root@server7 ~]#teamdctl team0 state
[root@server7 ~]#nmcli connection add con-name team0-port2 type team-slave ifname eno50332216 master team0
[root@server7 ~]#teamdctl team0 state
[root@server7 ~]#ifdown eno33554992
[root@server7 ~]#teamdctl team0 state
[root@server7 ~]#nmcli connection up eno33554992
[root@server7 ~]#nmcli connection up team0-port1
[root@server7 ~]#teamdctl team0 state
[root@server7 ~]#nmcli connection down team0-port2
[root@server7 ~]#teamdctl team0 state
[root@server7 ~]#nmcli connection up team0-port2
[root@server7 ~]#nmcli teamdctl team0 state

Note : Do ping command ping 192.168.0.254 -t from another terminal to check status

Do the same for desktop machine also....

8) SMTP configuration

--->configure the SMTP mail service on serverX and desktopX which only reply mail from local system through station.network0.example.com
--->all outgoing mail have ther sender domain at example.com ensure that mail should not store locally.
--->Verify the mail server is woring by sender mail to a sirat user.

Solution:

[root@server7 ~]#yum install postfix
[root@server7 ~]#systemctl enable postfix
[root@server7 ~]#systemctl start postfix

--Allow smtp port into firewall---

[root@server7 ~]firewall-cmd --permanent --add-service=smtp
[root@server7 ~]firewall-cmd --reload
[root@server7 ~]firewall-cmd --list-ports
[root@server7 ~]vim /etc/postfix/main.conf

inet_interface=localhost
mydestination=
myorigin=example.com
relayhost=[station.network0.example.com]
mynetworks=127.0.0.0/8,[::1]/128
local_transport=error:local delivery disabled

[root@server7 ~]#systemctl start postfix
[root@server7 ~]#useradd sirat
[root@server7 ~]#mail -V sirat@server7.example.com   [send a test mail to sirat user]

[root@server7 ~]#tail -f /var/log/maillog [check mail status]

17) script

--->create a script on serverX called /root/random with the following details
--->when run as /root/random Postconf, should bring the output as "Postroll"
--->when run as /root/random Postroll, should bring the output as "Postconf"
--->when run with only other argument or wihout argument, should bring the stderr as
"/root/random Postconf | Postroll"

Solution:

[root@server7 ~]#vim /root/random
#!/bin/bash
case $@ in
postconf ) echo "Postroll";;
Postroll ) echo "postconf";;
         *) echo "/root/random postconf | Postroll";;
esac

[root@server7 ~]#chmod a+x /root/random

18) script 

--->create a script on serverX called /root/createusers
--->when this script is called with the test file argument, it should add all the users from the file
--->downloaded the fire from http://station.network0.example.com/pub/testfile
--->all user should have the login shell as /bin/false, passwd not required.
--->when this script is called wih anyother argument, it should print the message "Input File Not Found"
--->When this script is run without any argument, it should dissplay "Usage "/root/createuser"
Note:- If the users are added no need to delete.

Solution:

#wget http://classroom.example.com/pub/testfile

[root@server7 ~]#vim /root/createusers

#!/bin/bash
a=""
case "$@" in
testfile ) for b in `cat testfile`
do
useradd -s /bin/false $b;
done;;
$a ) echo "Usage:/root/createusers";;
* ) echo "Input file Not Found";;
esac

[root@server7 ~]#chmod a+x /root/createusers


19) Configure SCSI storage. (Target CLI)

--->create a new 1 GB iscsi_block target on your serverX.example.com
--->The server should export on iscsi disk called iqn.2014.11.com.example.serverX.
--->This target should be only be available allowd to clients with an IQN of iqn.2014.11.com.example.desktopX.

Solution:

Server-Vm
--------
[root@server7 ~]#yum install targetcli* -y
[root@server7 ~]#systemctl enable target.service
[root@server7 ~]#systemctl start target.service
[root@server7 ~]#firewall-cmd --permanent --add-port=3260/tcp
[root@server7 ~]#firewall-cmd --reload
[root@server7 ~]#fdisk /dev/vdb   [Create 1GB new partition]
:n,:p,:1,:Enter,:+1G,:w
#partprobe /dev/vdb
#cat /proc/partitions
#targetcli
>ls
>cd /backstores/block
>create block1 /dev/vdb1
>cd /iscsi
>create iqn.2014-10.com.example:serverX
>cd /iscsi/iqn.2014-10.com.example/tpg1/acls
>create iqn.2014-10.com.example:desktopX
>cd /iscsi/iqn.2014-10.com.example/tpg1/luns
>create /backstore/block/block1
>cd /iscsi/iqn.2014-10.com.example/tpg1/portals
>create 172.25.X.11/3260      ------->( server ip)
>exit


#systemctl restart target.service

20) ISCSI initiator
-The serverX.example.com provides an iscsi port (3260). connect the disk with desktopX.example.com
and configure filesystem with the following requirements,
-create 800MB partition on ISCSI blcok device and assign the filesystem as xfs.
-Mount the volume under /mnt/initiator at the system boot time.
The filesystem should contain the copy of http://classroom.example.com/pub/iscsi.txt
The file should be owned by root with 0644 permission Note: don't modify the content.

Desktop-Vm
----------
[root@server7 ~]#yum install iscsi-initiator-utils -y
[root@server7 ~]#systemctl enable iscsi.service iscsid.service
[root@server7 ~]#systemctl start iscsi.service iscsid.service

[root@server7 ~]#vim /etc/iscsi/initiatorname.iscsi
InitiatorName=iqn.2014-10.com.example:desktopX

:wq

[root@server7 ~]#systemctl restart iscsi.service iscsid.service

[root@server7 ~]#systemctl start iscsi.service
[root@server7 ~]#systemctl start iscsid.service

man iscsiadm -- search with /examples and take discoverydb and login commands and modify the ipaddress.

[root@server7 ~]#iscsiadm --mode discoverydb --type sendtargets --portal 172.25.11.11 --discover
[root@server7 ~]#iscsiadm --mode node --targetname iqn.2014-06.com.example:server11 --portal 172.25.11.11:3260 --login
cat /proc/partitions
[root@server7 ~]#fdisk /dev/sdc
n,p,1,Enter,+200M,w
[root@server7 ~]#partprobe /dev/sdc
[root@server7 ~]#blkid
[root@server7 ~]#vim /etc/fstab
UUID= /media ext4 _netdev 0 0
:wq
=================

Default permission of file and directory in Linux / UNIX

What is UMASK

UMASK (User Mask or User file creation MASK) is the default permission of file and directory in Linux or UNIX. There are three types of permission for every file and directory (read, write and execute) for three types of user (Owner, Groups and Others).

[wasi@saidrasel ~]]$ mkdir cde

[wasi@saidrasel ~]]$ touch abc

[wasi@saidrasel ~]$ ls -l abc
-rw-rw-r--. 1 wasi wasi 0 Dec 26 11:12 abc

In the above example

• User (wasi) has read,write permission
• Group has read, write permission
• Others have read permission

Three file permissions:

read: permission to read the contents of file.
write: permission to write to the file.
execute: permission to execute the file as a program/script.

Three directory permissions:

read: permission to read the contents of directory ( view files and sub-directories in that directory ).
write: permission to write in to the directory. ( create files and sub-directories in that directory )
execute: permission to enter into that directory.

Numeric values for the read, write and execute permissions:

read--4
write--2
execute--1

[wasi@saidrasel ~]$ ls -l abc
-rw-rw-r--. 1 wasi wasi 0 Dec 26 11:12 abc

drwxrwxr-x. 2 wasi wasi 6 Dec 26 11:31 cde

So the numeric value permission for this file is-- 4+2 4+2 4 --->664

and the numeric value permission for the directory is-- 4+2+1 4+2+1 4+1 --->775

Umask is responsible for the default permission

[wasi@saidrasel ~]$ umask
0002
[wasi@saidrasel ~]$

Final default permission for a file is calculated as shown below:

Default file permission: 666
Default umask : 002
Final default file permission: 664 (666-002)

Final default permission for a directory is calculated as shown below:

Default directory permission: 777
Default umask: 002
Final default directory permission: 775 (777-002)

We can find umask value setting from /etc/bashrc or /etc/profile

How to set access permission in a file for specific user in Linux

Files and directories have permission sets for the owner of the file, the group associated with the file, and all other users for the system. However, these permission sets have limitations. For example, different permissions cannot be configured for different users. Thus, Access Control Lists (ACLs) were implemented.

[root@saidrasel]# ll a

-rw-r--r--. 1 root root 0 Dec 25 22:56 a

Above permission means ---file owner is root have permission rw (read,write), group root have permission r (read) and other have permission r (read). Following example showing in details

[root@saidrasel]# getfacl a

# file: a

# owner: root

# group: root

user::rw-

group::r--

other::r--

Now we will set permission in file a for specific user wasi, so for this we need to create a user named wasi

[root@saidrasel]# useradd wasi

[root@saidrasel]# passwd wasi

Changing password for user wasi.

New password: 

Now we will set rwx (read,write and execute) permission for new user wasi

[root@saidrasel]# setfacl -m u:wasi:rwx a

or

[root@saidrasel]# setfacl -m u:wasi:rwx /root/Desktop/a       [for absolute path]

 Now we can check the permission of file a for user wasi

[root@saidrasel]# getfacl a

# file: a

# owner: root

# group: root

user::rw-

user:wasi:rwx

group::r--

mask::rwx

other::r--

[root@saidrasel]#

Thats it..........

How to Clear Cache Memory in Linux

Find Memory Status

[root@localhost Desktop]# free -m
             total       used       free     shared    buffers     cached
Mem:           987        915         71          7          0        395
-/+ buffers/cache:        519        467
Swap:         1023          0       1023

In this example the total amount of available memory is 987 M. 519 M are used by processes and 467 M are free for other applications. Do not get confused by the first line which shows that 71 M are free! If you look at the usage figures you can see that most of the memory use is for buffers and cache. Linux always tries to use RAM to speed up disk operations by using available memory for buffers (file system metadata) and cache (pages with actual contents of files or block devices). This helps the system to run faster because disk information is already in memory which saves I/O operations. If space is needed by programs or applications like Oracle, then Linux will free up the buffers and cache to yield memory for the applications. If your system runs for a while you will usually see a small number under the field "free" on the first line.


Find Cache Memory uses in Linux

Use free command to find out cache memory uses by Linux system. Output of free command is like below

Last column is showing cached memory (  395 MB) by system. -m option is used for showing memory details in MB’s.


[root@localhost Desktop]# free -m
             total       used       free     shared    buffers     cached
Mem:           987        915         71          7          0        395
-/+ buffers/cache:        519        467
Swap:         1023          0       1023

Following command to see much detailed information about current memory usage in 3 second interval:

[root@localhost Desktop]# watch -n 3 cat /proc/meminfo

Every 3.0s: cat /proc/meminfo                                                          Wed Dec 23 23:28:53 2015

MemTotal:        1010884 kB
MemFree:          353384 kB
MemAvailable:     367148 kB
Buffers:              40 kB
Cached:           123052 kB
SwapCached:            0 kB
Active:           427352 kB
Inactive:          83868 kB
Active(anon):     385120 kB
Inactive(anon):    11240 kB
Active(file):   42232 kB
Inactive(file):    72628 kB
Unevictable:           0 kB
Mlocked:               0 kB
SwapTotal: 1048572 kB
SwapFree:        1048572 kB
Dirty:                40 kB
Writeback:             0 kB
AnonPages:        388152 kB
Mapped:            95736 kB
Shmem:              8216 kB
Slab:              67208 kB

1. Freeing pagecache only use following command

[root@localhost Desktop]# sync; echo 1 > /proc/sys/vm/drop_caches


[root@localhost Desktop]# free -m
             total       used       free     shared    buffers     cached
Mem:           987        611        375          7          0         92
-/+ buffers/cache:        518        468
Swap:         1023          0       1023

2. Freeing dentries and inodes use following command

[root@localhost Desktop]# sync; echo 2 > /proc/sys/vm/drop_caches


[root@localhost Desktop]# free -m
             total       used       free     shared    buffers     cached
Mem:           987        594        392          7          0         93
-/+ buffers/cache:        501        485
Swap:         1023          0       1023

3. Freeing pagecache, dentries and inodes in cache memory

[root@localhost Desktop]# sync; echo 3 > /proc/sys/vm/drop_caches


[root@localhost Desktop]# free -m
             total       used       free     shared    buffers     cached
Mem:           987        596        391          7          0         91
-/+ buffers/cache:        504        482
Swap:         1023          0       1023
[root@localhost Desktop]#

4. Schedule Cron to Flush Cache Regularly

If we want to schedule following in crontab to automatically flush cache on regular interval.

# crontab -l

0 * * *  * sync; echo 3 > /proc/sys/vm/drop_caches

The above cron will execute on every hour and flushes the cached memory on system.

Find empty file or directory in Linux

### Find empty file from current directory ###

[root@localhost ~]# find -type f -empty
./.cache/abrt/applet_dirlist
./.local/share/gnome-settings-daemon/input-sources-converted
./.local/share/folks/relationships.ini
./.local/share/.converted-launchers
./.local/share/tracker/data/.meta.isrunning
./.local/share/keyrings/user.keystore.HQQ99X
./.local/share/keyrings/user.keystore.ZUKY9X
./.local/share/keyrings/user.keystore.VG4S9X
./.local/share/keyrings/user.keystore.G00V9X
./.local/share/keyrings/user.keystore.681AAY
./.local/share/keyrings/user.keystore.A15Y9X
./.local/share/keyrings/user.keystore.7NT89X
./test/saidrasel.lst

### Find empty file from specific directory ###

[root@localhost ~]# find /root/test -type f -empty
/root/test/saidrasel.lst
[root@localhost ~]#
### Find empty directory from current location ###
[root@localhost ~]# find  -type d -empty
./.cache/evolution/addressbook/trash
./.cache/evolution/calendar/trash
./.cache/evolution/mail/trash
./.cache/evolution/memos/trash
./.cache/evolution/sources/trash
./.cache/evolution/tasks/trash
./.cache/folks/avatars
./.config/imsettings
./.config/abrt

### Find empty directory from specific location ###

[root@localhost ~]# mkdir -p /home/rasel/test

[root@localhost ~]# find /home/rasel/ -type d -empty
/home/rasel/.mozilla/extensions
/home/rasel/.mozilla/plugins
/home/rasel/.config/abrt
/home/rasel/test
[root@localhost ~]#

[root@localhost ~]# mkdir -p /home/rasel/test/abc

[root@localhost ~]# find /home/rasel/ -type d -empty
/home/rasel/.mozilla/extensions
/home/rasel/.mozilla/plugins
/home/rasel/.config/abrt
/home/rasel/test/abc
[root@localhost ~]#

### Remove empty directory ###

Create empty directory using following command

[root@localhost rasel]# pwd
/home/rasel
[root@localhost rasel]# mkdir test
[root@localhost rasel]# cd test/
[root@localhost test]# mkdir abc
[root@localhost test]# pwd
/home/rasel/test
[root@localhost test]# cd /root/
[root@localhost ~]# pwd
/root
[root@localhost ~]# find /home/rasel/ -type d -empty
/home/rasel/test/abc
 
[root@localhost ~]# ls -la /home/rasel/test/
total 4
drwxr-xr-x. 3 root  root    16 Dec 21 16:44 .
drwx------. 4 rasel rasel 4096 Dec 21 16:44 ..
drwxr-xr-x. 2 root  root     6 Dec 21 16:44 abc

Now remove the empty directory

[root@localhost ~]# find /home/rasel/test/ -type d -empty -exec rmdir {} \;
find: ‘/home/rasel/test/abc’: No such file or directory

[root@localhost ~]# ls -la /home/rasel/test/
total 4
drwxr-xr-x. 2 root  root     6 Dec 21 16:45 .
drwx------. 4 rasel rasel 4096 Dec 21 16:44 ..
[root@localhost ~]#

Locate command in Linux

locate command search very quickly, because  locate does not search the files on disk rather it searches for file paths in a database. The locate database file is located at:

[root@localhost test]# locate mlocate.db
/usr/share/man/man5/mlocate.db.5.gz
/var/lib/mlocate/mlocate.db/var/lib/mlocate/mlocate.db.UY1Pjl
[root@localhost test]#


[root@localhost test]# locate sysctl.conf
/etc/sysctl.conf
/etc/sysctl.d/99-sysctl.conf
/usr/share/man/man5/sysctl.conf.5.gz
[root@localhost test]#

Now create a directory and touch a file

[root@localhost Desktop]# mkdir -p /root/test
[root@localhost Desktop]# touch /root/test/saidrasel.lst
[root@localhost test]# locate saidrasel*

Now execute the locate command to find "saidrasel.lst" file but could'nt get

[root@localhost test]# locate saidrasel.lst


Now execute the updatedb command,  it scans the whole system and updates the mlocate.db database file.

[root@localhost test]# updatedb
[root@localhost test]# locate saidrasel.lst
/root/test/saidrasel.lst
[root@localhost test]#

Note: So the limitation of the "locate" command is its dependency on the database which can be updated by another utility "updated". Hence, in order to get the latest and reliable results from "locate" command the database on which it works should be updated at regular intervals.

Find file based on access/modification time

We can find files based on following three file time attribute.

Access time of the file: Access time gets updated when the file accessed.
Modification time of the file: Modification time gets updated when the file content modified.
Change time of the file: Change time gets updated when the inode data changes

###Find files whose content got updated within last 1 hour###

[root@stelar_test oracle]# find /home/oracle -mmin -60
/home/oracle
/home/oracle/SaidRasel.c
[root@stelar_test oracle]#

-mmin n File’s data was last modified n minutes ago.
-mtime n File’s data was last modified n*24 hours ago.

[root@stelar_test oracle]# find /home/oracle -mtime -1
/home/oracle
/home/oracle/SaidRasel.c
[root@stelar_test oracle]#

###Find files which got accessed before 1 hour###

-amin n File was last accessed n minutes ago-atime n File was last accessed n*24 hours ago

Finds all the files (under /home/oracle) that got accessed within the last 24 hours (1 day).

[root@stelar_test oracle]# find /home/oracle -atime -1
/home/oracle/.ssh
/home/oracle/.oracle
/home/oracle/.oracle/logs
/home/oracle/.local
/home/oracle/.local/share
/home/oracle/.local/share/applications
/home/oracle/.local/share/gvfs-metadata
/home/oracle/.thumbnails
/home/oracle/.thumbnails/normal
/home/oracle/Downloads
/home/oracle/.gvfs
/home/oracle/.spice-vdagent
/home/oracle/.bash_profile
/home/oracle/.cache
/home/oracle/Templates
/home/oracle/tomcat jdk
/home/oracle/.dbus
/home/oracle/.dbus/session-bus

Finds all the files (under /root/test/backup) that got accessed within the last 24 hours (1 day).


[root@stelar_test oracle]# find /root/test/backup/ -atime -1
/root/test/backup/
/root/test/backup/Program.c
/root/test/backup/mycprogram.c
/root/test/backup/MyCProgram.c
/root/test/backup/saidrasel.c
/root/test/backup/MybashProgram.sh
[root@stelar_test oracle]#

Find files in the current directory and sub-directories, which got accessed within last 1 hour (60 minutes)

[root@stelar_test oracle]#  find -amin -60
.
./SaidRasel.c
./.bash_history
[root@stelar_test oracle]#

Find files in the current directory and sub-directories, which got accessed within last 1 hour (60 minutes)

[root@stelar_test oracle]#  find /home/oracle/ -amin -60
/home/oracle/
/home/oracle/SaidRasel.c
/home/oracle/.bash_history
[root@stelar_test oracle]#
-amin n File was last accessed n minutes ago
-atime n File was last accessed n*24 hours ago

###Find files which got changed before 1 hour###

-cmin n File’s status was last changed n minutes ago.
-ctime n File’s status was last changed n*24 hours ago.

find files in the current directory and sub-directories, which changed within last 1 hour (60 minutes)

[root@stelar_test oracle]#  find /home/oracle/ -cmin -60
/home/oracle/
/home/oracle/SaidRasel.c
/home/oracle/.bash_history
[root@stelar_test oracle]#  find . -cmin -60
.
./SaidRasel.c
./.bash_history
[root@stelar_test oracle]#

finds all the files (under /root/test/backup/) that got changed within the last 24 hours (1 day).

[root@stelar_test oracle]# find /root/test/backup/ -ctime -1
/root/test/backup/
/root/test/backup/Program.c
/root/test/backup/mycprogram.c
/root/test/backup/MyCProgram.c
/root/test/backup/saidrasel.c
/root/test/backup/MybashProgram.sh
[root@stelar_test oracle]#



Reference :
http://www.thegeekstuff.com/2009/06/15-practical-unix-linux-find-command-examples-part-2/

Find files using file name in Linux

create two file named saidrasel.c into current directory /root/test and /root/test/backup directory

[root@stelar_test test]# touch saidrasel.c
[root@stelar_test test]# cd backup/
[root@stelar_test backup]# touch saidrasel.c


Now execute the find command to search saidrasel.c file from /root/test location
[root@stelar_test test]#pwd
/root/test
[root@stelar_test test]# find -name saidrasel.c
./backup/saidrasel.c
./saidrasel.c
[root@stelar_test test]#

Now execute the find command to search saidrasel.c file from / location

[root@stelar_test /]# find -name saidrasel.c
./root/test/backup/saidrasel.c
./root/test/saidrasel.c
[root@stelar_test /]#

Now execute the find command to search saidrasel.c file from any location

[root@stelar_test oracle]# pwd
/home/oracle

Following search will start from / (root) location

[root@stelar_test oracle]# find / -name  saidrasel.c
/root/test/backup/saidrasel.c
/root/test/saidrasel.c
[root@stelar_test oracle]#

[root@stelar_test oracle]# find / -name  saidrasel*
/root/test/backup/saidrasel.c
/root/test/saidrasel.c

[root@stelar_test oracle]# find / -name  saidrase*
/root/test/backup/saidrasel.c
/root/test/saidrasel.c

[root@stelar_test oracle]# find / -name  saidra*
/root/test/backup/saidrasel.c
/root/test/saidrasel.c
[root@stelar_test oracle]#

Find Files Using Name and Ignoring Case


[root@stelar_test oracle]# find / -iname  "SaidRasel.c"
/home/oracle/SaidRasel.c
/root/test/SaidRasel.c
/root/test/backup/saidrasel.c
/root/test/saidrasel.c
[root@stelar_test oracle]#

[root@stelar_test oracle]# find / -iname  "saidrasel.c"
/home/oracle/SaidRasel.c
/root/test/SaidRasel.c
/root/test/backup/saidrasel.c
/root/test/saidrasel.c
[root@stelar_test oracle]#

Directory or File Permission in Linux

For Example---

[oracle@sbldb2 ~]$ ll
total 516
-rw-r--r-- 1 oracle oinstall 235340 Nov  2 11:50 02112015.lst
-rw-r--r-- 1 oracle oinstall 257702 Sep  8  2014 awrrpt_1_7407_7409.txt
drwxr-xr-x 2 oracle oinstall   4096 Mar 12  2014 Desktop
-rw-r--r-- 1 oracle oinstall    364 Apr  1  2014 Dhaka.bkp
drwxr-xr-x 3 oracle oinstall   4096 Mar 23  2014 oradiag_oracle
drwxr-xr-x 4 oracle oinstall   4096 Sep  2 15:45 rman
-rw-r--r-- 1 oracle oinstall   3965 Jan  5  2015 tuning.sql

Total 10 fields in prefix of every files and directory as above

Here
user ---> oracle
group ---> oinstall

-rwxr-xr-x

1st filed represents ---> Directory
2nd,3rd and 4th filed represent ---> Owner Permission
5th,6th and 7th filed represent ---> Group Member Permission
8th,9th and 10th field represent ---> Other Permission

You can setup following mode on each files. In a Linux and UNIX set of permissions is called as mode:

Read (r)
Write (w)
Execute (x)

Linux Read mode permissions

--Read access on a file allows you to view file
--Read access on a directory allows you to view directory contents with ls command
Write mode permissions

--Write access on a file allows you to write to file
--Write access on a directory allows you to remove or add new files
Execute mode permissions

--Execute access on a file allows to run program or script
--Execute access on a directory allows you access file in the directory

Octal numbers and permissions

You can use octal number to represent mode/permission:
r: 4
w: 2
x: 1

Use above method to calculate permission for group and others. Let us say you wish to give full permission to owner, read & execute permission to group, and read only permission to others, then you need to calculate permission as follows:

-rwx-rw--x-- 1 oracle oinstall   3965 Jan  5  2015 tuning.sql

User (oracle) = r+w+x = 4+2+1 = 7
Group (oinstall) = r+w = 4+2+0 = 6
Others = r= 4+0+0 = 4

Effective permission is 764.

Server uptime command in Linux

[root@stelar_test ~]# uptime
 13:37:01 up 15 days, 16:47,  1 user,  load average: 0.11, 0.05, 0.01

 The uptime command gives a one line display of the following information.


-The current time (13:37:01)
-How long the system has been running (up 15 days)
-How many users are currently logged on (1 user)
-The system load averages for the past 1, 5, and 15 minutes (0.11, 0.05, 0.01)

This is the same information contained in the header line displayed by the w and top commands:

[root@stelar_test ~]# w
 13:37:05 up 15 days, 16:47,  1 user,  load average: 0.10, 0.05, 0.01
USER     TTY      FROM              LOGIN@   IDLE   JCPU   PCPU WHAT
root     pts/0    192.168.201.94   11:41    0.00s  0.05s  0.00s w

[root@stelar_test ~]# top
top - 13:37:51 up 15 days, 16:47,  1 user,  load average: 0.05, 0.04, 0.00
Tasks: 208 total,   1 running, 207 sleeping,   0 stopped,   0 zombie
Cpu(s):  0.5%us,  0.4%sy,  0.0%ni, 98.0%id,  1.1%wa,  0.0%hi,  0.1%si,  0.0%st
Mem:   4791876k total,  4635552k used,   156324k free,    81896k buffers
Swap:  8388600k total,    57012k used,  8331588k free,  3932264k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
26884 root      20   0 15084 1188  832 R  2.0  0.0   0:00.01 top
    1 root      20   0 19400  788  580 S  0.0  0.0   0:08.90 init
    2 root      20   0     0    0    0 S  0.0  0.0   0:00.00 kthreadd
    3 root      RT   0     0    0    0 S  0.0  0.0   0:00.02 migration/0
    4 root      20   0     0    0    0 S  0.0  0.0   0:00.89 ksoftirqd/0
    5 root      RT   0     0    0    0 S  0.0  0.0   0:00.00 migration/0
    6 root      RT   0     0    0    0 S  0.0  0.0   0:00.00 watchdog/0
    7 root      RT   0     0    0    0 S  0.0  0.0   0:00.03 migration/1
    8 root      RT   0     0    0    0 S  0.0  0.0   0:00.00 migration/1
    9 root      20   0     0    0    0 S  0.0  0.0   0:02.85 ksoftirqd/1
   10 root      RT   0     0    0    0 S  0.0  0.0   0:00.00 watchdog/1
   11 root      20   0     0    0    0 S  0.0  0.0   0:02.38 events/0
   12 root      20   0     0    0    0 S  0.0  0.0   7:39.35 events/1
   13 root      20   0     0    0    0 S  0.0  0.0   0:00.00 cpuset
   14 root      20   0     0    0    0 S  0.0  0.0   0:00.00 khelper

Booting Processes/Sequences of RHEL 7

A quick view of booting sequence:

• Power on
• CPU jumps to BIOS
• BIOS runs POST
• Finds first bootable device
• Load and execute MBR
• Load OS
• User prompt

This a rough idea what happens in Linux booting. Below are the detailed stages in Linux Booting process.

Stages of Booting:

1)System startup(Hardware )

2)Boot loader Stage 1 (MBR loading)

3)Boot loader Stage 2 (GRUB loader)

4)Kernel

5)INIT

6)User prompt

Step 1: System startup

This is the first stage of booting process. When you power on/Restart your machine the power is supplied to SMPS (switched-mode power supply) which converts AC to DC. The DC power is supplied to all the devices connected to that machine such as Motherboard HDD's, CD/DVD-ROM, Mouse, keyboard etc. The most intelligent device in the computer is Processor(CPU), when supplied with power will start running its sequence operations stored in its memory. The first instruction it will run is to pass control to BIOS(Basic Input/Output System) to do POST(Power On Self Test). Once the control goes to BIOS it will take care of two things

Run POST operation.

Selecting first Boot device.

POST operation: POST is a processes of checking hardware availability. BIOS will have a list of all devices which are present in previous system boot. In order to check if a hardware is available for the present booting or not it will send an electric pulse to each and every device in the list that it already have. If an electrical pulse is returned from that device it will come to a conclusion the hardware is working fine and ready for use. If it does not receive a single from a particular device it will treat that device as faulty or it was removed from the system. If any new hardware is attached to the system it will do the same operation to find if its available or not. The new list will be stored in BIOS memory for next boot.

Selecting First Boot Device: Once the POST is completed BIOS will have the list of devices available. BIOS memory will have the next steps details like what is the first boot device it has to select etc. It will select the first boot device and gives back the control to Processor(CPU). Suppose if it does not find first boot device, it will check for next boot device, if not third and so on. If BIOS do not find any boot device it will alert user stating "No boot device found".

Step 2: The Master Boot Record

In case of hard disks and many other mass storage media, the boot sector is MBR. MBR consists of 512 bytes at the first sector of the hard disk. It is important to note that MBR is not located inside any partition. MBR precedes the first partition. The layout of MBR is as follows:

• First 446 bytes contain bootable code.
• Next 64 bytes contain partition information for 4 partitions (16x4). That is why the hard disks can have only 4 primary partitions, as the MBR can store information for 4 partitions only. So if you need more than 4 partitions on the hard disk, one of the primary partition has to be made extended, and out of this extended partition, logical partitions are created.
• Last 2 bytes are for MBR signature, also called magic number. (Thus total of 446 + 64 + 2 = 512 bytes).

|=================|======|======|======|======|===|
| 446 | 16 | 16 | 16 | 16 | 2 |
|=================|======|======|======|======|===|

The first 446 bytes of MBR contain the code that locates the partition to boot from. The rest of booting process takes place from that partition. This partition contains a software program for booting the system called the 'bootloader'.

Step 3: Boot loader Stage 2 (GRUB loader)

Once the Bootloader stage 1 is completed and able to find the actual bootloader location, Stage 1 bootloader start second stage by loading Bootloader into memory. In this stage GRUB(Grand Unified Bootloader) which is located in the first 30 kilobytes of hard disk immediately following the MBR is loaded into RAM for reading its configuration and displays the GRUB boot menu (where the user can manually specify the boot parameters) to the user. GRUB loads the user-selected (or default) kernel into memory and passes control on to the kernel. If user do not select the OS, after a defined timeout GRUB will load the default kernel in the memory for starting it.

Step 4: Kernel

Once the control is given to kernel which is the central part of all your OS and act as a mediator of hardware and software components. Kernel once loaded into to RAM it always resides on RAM until the machine is shutdown. Once the Kernel starts its operations the first thing it do is executing INIT process.

Step 5: INIT

‘init’ is the first process started by kernel (initialization process). It is parent of all processes. The PID (Process ID) of init process is always 1. This process persists till the computer halts. It is responsible for the whole state of system. The settings for this process are stored in its configuration file, /etc/inittab (system initialization table).Before diving deeper into the details of this file and proceeding any further with the boot process, let’s discuss about runlevels

Step 6: Runlevels

Runlevel is the state in which a system boots. It can boot in a single user mode, multiuser mode, with networking, and with graphics etc. Following are the default runlevels defined by Linux:

0: Halt or shutdown the system

1: Single user mode

2: Multi-user mode, without networking

3: Full multi user mode, with NFS (typical for servers)

4: Officially not defined; Unused

5: Full multi user with NFS and graphics (typical for desktops)

6: Reboot

References:

http://linoxide.com/booting/boot-process-of-linux-in-detail/

http://www.linuxnix.com/linux-booting-process-explained/

Step by step to configure Samba in RHEL 6

Step 1: Install necessary RPM

[root@stelar_test repodata]# ls -lrt sam*
-r--r--r--. 1 root root    30556 Aug 17  2010 samyak-malayalam-fonts-1.2.1-9.el6.noarch.rpm
-r--r--r--. 1 root root    49496 Aug 17  2010 samyak-gujarati-fonts-1.2.1-9.el6.noarch.rpm
-r--r--r--. 1 root root    18328 Aug 17  2010 samyak-fonts-common-1.2.1-9.el6.noarch.rpm
-r--r--r--. 1 root root    61720 Aug 17  2010 samyak-devanagari-fonts-1.2.1-9.el6.noarch.rpm
-r--r--r--. 1 root root    26936 Aug 17  2010 samyak-tamil-fonts-1.2.1-9.el6.noarch.rpm
-r--r--r--. 1 root root    66000 Aug 17  2010 samyak-oriya-fonts-1.2.1-9.el6.noarch.rpm
-r--r--r--. 1 root root  1116684 Nov  3  2011 samba-winbind-clients-3.5.10-114.el6.i686.rpm
-r--r--r--. 1 root root 13918292 Nov  3  2011 samba-common-3.5.10-114.el6.i686.rpm
-r--r--r--. 1 root root  1119920 Nov  3  2011 samba-winbind-clients-3.5.10-114.el6.x86_64.rpm
-r--r--r--. 1 root root 13999076 Nov  3  2011 samba-common-3.5.10-114.el6.x86_64.rpm
-r--r--r--. 1 root root  5217032 Nov  3  2011 samba-3.5.10-114.el6.x86_64.rpm
-r--r--r--. 1 root root  3726432 Nov  3  2011 samba-winbind-3.5.10-114.el6.x86_64.rpm
-r--r--r--. 1 root root 11488144 Nov  3  2011 samba-client-3.5.10-114.el6.x86_64.rpm
[root@stelar_test repodata]# rpm -Uvh samba-3.5.10-114.el6.x86_64.rpm
warning: samba-3.5.10-114.el6.x86_64.rpm: Header V3 RSA/SHA256 Signature, key ID fd431d51: NOKEY
Preparing...                ########################################### [100%]
   1:samba                  ########################################### [100%]
[root@stelar_test repodata]# rpm -Uvh samba-common-3.5.10-114.el6.x86_64.rpm
warning: samba-common-3.5.10-114.el6.x86_64.rpm: Header V3 RSA/SHA256 Signature, key ID fd431d51: NOKEY
Preparing...                ########################################### [100%]
        package samba-common-0:3.5.10-114.el6.x86_64 is already installed
[root@stelar_test repodata]# rpm -Uvh samba-winbind-3.5.10-114.el6.x86_64.rpm
warning: samba-winbind-3.5.10-114.el6.x86_64.rpm: Header V3 RSA/SHA256 Signature, key ID fd431d51: NOKEY
Preparing...                ########################################### [100%]
   1:samba-winbind          ########################################### [100%]
 
Samba Daemons
For Samba we need three services to run, one optional and two required
Service Daemons Description
Required smb smbd (SMB/CIFS Server) main samba service which provide user authentication and authorization and file and printer sharing
Required nmb nmbd (NetBIOS name server) Resources browsing
Optional winbind winbindd For host and user name resolution

Step 2: If you have just installed RPM than these service would be stopped.


 
[root@stelar_test repodata]# service smb status
smbd is stopped
[root@stelar_test repodata]# service nmb status
nmbd is stopped
[root@stelar_test repodata]# service winbind status
winbindd is stopped

Step 3: Start necessary services

[root@stelar_test repodata]# service smb start
Starting SMB services:                                     [  OK  ]
[root@stelar_test repodata]# service nmb start
Starting NMB services:                                     [  OK  ]
[root@stelar_test repodata]# service winbind start
Starting Winbind services:                                 [  OK  ]

Step 4: Make sure the services are running at the next time Linux is booted

[root@stelar_test repodata]# chkconfig smb on
[root@stelar_test repodata]# chkconfig nmb on
[root@stelar_test repodata]# chkconfig winbind on
[root@stelar_test repodata]#

Step 5: Creating Samba Test Directory and Files

mkdir /smbdemo

Step 6: Change the permissions on the new directory to 770 with the following command:

chmod 770 /smbdemo


Step 7: Adding the Samba User and Creating the Samba Group

# adduser administrator
# passwd administrator
Changing password for user administrator
New UNIX password: ********
Retype new UNIX password: ********
passwd: all authentication tokens updated successfully.


You must add users to the Samba database in order for them to have access to their home directory and other Samba shares.

Step 8: Now open main configuration file of Samba

[root@stelar_test pen]# vim /etc/samba/smb.conf

[backup_cbs_usb]

comment= Linux Share Samba
path=/mnt/pen
browsable=yes
guest ok=yes
read only=no
create mask=0755

Note : Change the security value to share

security = share
        passdb backend = tdbsam

Step 9: Now restart the samba service 

[root@stelar_test pen]# service smb restart
Shutting down SMB services:                                [  OK  ]
Starting SMB services:                                     [  OK  ]

Step 10: Now browse the samba directory from windows PC

\\192.168.10.177\backup_cbs_usb

Step by Step : How to configure YUM Server in RHEL6

Make directories yum/rhel6/repodata in the folder which you have chosen for repository.

For FTP server it would be /var/ftp/pub folder

[root@dpdcdb repodata]# mkdir -p /var/ftp/pub/yum/rhel6/repodata/

Copy all RPM from RHEL 6 DVD located in Packages folder to [root@dpdcdb repodata]#

[root@dpdcdb repodata]# cp -arf /media/RHEL_6.2\ x86_64\ Disc\ 1/Packages/*.rpm /var/ftp/pub/yum/rhel6/repodata/


root@dpdcdb repodata]# cp /media/RHEL_6.2\ x86_64\ Disc\ 1/repodata/*comps*.xml /var/ftp/pub/yum/rhel6/repodata/comps.xml
[root@dpdcdb repodata]#

[root@dpdcdb RHEL_6.2 x86_64 Disc 1]# cd Server/
[root@dpdcdb Server]# rpm -qa deltarpm
[root@dpdcdb Server]# rpm -qa python-deltarpm
[root@dpdcdb Server]# rpm -qa createrepo
[root@dpdcdb Server]# pwd
/media/RHEL_6.2 x86_64 Disc 1/Server
[root@dpdcdb Server]#
[root@dpdcdb Server]# cd /var/ftp/pub/yum/rhel6/repodata/
[root@dpdcdb repodata]# rpm -ivh deltarpm*
warning: deltarpm-3.5-0.5.20090913git.el6.x86_64.rpm: Header V3 RSA/SHA256 Signature, key ID fd431d51: NOKEY
Preparing...                ########################################### [100%]
   1:deltarpm               ########################################### [100%]
[root@dpdcdb repodata]#
[root@dpdcdb repodata]# rpm -ivh python-deltarpm*
warning: python-deltarpm-3.5-0.5.20090913git.el6.x86_64.rpm: Header V3 RSA/SHA256 Signature, key ID fd431d51: NOKEY
Preparing...                ########################################### [100%]
   1:python-deltarpm        ########################################### [100%]
[root@dpdcdb repodata]#
[root@dpdcdb repodata]# rpm -ivh createrepo*
warning: createrepo-0.9.8-4.el6.noarch.rpm: Header V3 RSA/SHA256 Signature, key ID fd431d51: NOKEY
Preparing...                ########################################### [100%]
   1:createrepo             ########################################### [100%]
[root@dpdcdb repodata]#

[root@dpdcdb repodata]# rpm -qa createrepo
createrepo-0.9.8-4.el6.noarch
[root@dpdcdb repodata]# rpm -qa python-deltarpm
python-deltarpm-3.5-0.5.20090913git.el6.x86_64
[root@dpdcdb repodata]# rpm -qa deltarpm
deltarpm-3.5-0.5.20090913git.el6.x86_64
[root@dpdcdb repodata]#

Change directory to /var/ftp/pub/yum/rhel6

[root@dpdcdb repodata]# cd ../
[root@dpdcdb rhel6]# ll
total 248
drwxr-xr-x. 2 root root 253952 May 26 15:50 repodata
[root@dpdcdb rhel6]#

Generate local repository files from repodata folder [ repodata folder :- which contain all RPM copied from RHEL6 DVD] to current folder [rhel6]

[root@dpdcdb rhel6]# createrepo -g repodata/comps
comps-extras-17.8-1.el6.noarch.rpm  comps.xml

[root@dpdcdb rhel6]# createrepo -g repodata/comps.xml .
 979/3596 - repodata/oxygen-icon-theme-4.3.4-2.el6.noarch.rpm
iso-8859-1 encoding on Ville Skyttä - 2.8.2-2

3596/3596 - repodata/qpid-cpp-client-0.12-6.el6.i686.rpm
Saving Primary metadata
Saving file lists metadata
Saving other metadata
[root@dpdcdb rhel6]#


[root@dpdcdb rhel6]# vim /etc/yum.repos.d/server.repo

[server]
name=rhel6
baseurl=file:///var/ftp/pub/yum/rhel6
enabled=1
gpgcheck=0


[root@dpdcdb rhel6]# vim /etc/yum.repos.d/server.repo
[root@dpdcdb rhel6]# yum clean all
Loaded plugins: product-id, refresh-packagekit, security, subscription-manager
Updating certificate-based repositories.
Cleaning repos: InstallMedia server
Cleaning up Everything
[root@dpdcdb rhel6]#


[root@dpdcdb rhel6]# yum makechace
Loaded plugins: product-id, refresh-packagekit, security, subscription-manager
Updating certificate-based repositories.
No such command: makechace. Please use /usr/bin/yum --help
[root@dpdcdb rhel6]#

Configure Yum repository in Linux

Create a folder in the server.

mkdir -p /var/ftp/pub/Server

Copy all RPMs from Linux DVD to Here.

Create the base repository headers:

cd /var/ftp/pub/Server/
rpm –ivh createrepo*

Paste database file to /tmp location

cd repodata/
cp comps* /tmp/comps.xml

Create repository

createrepo –g /tmp/comps.xml /var/ftp/pub/Server

Add your local repo to the list

cd /etc/yum.repos.d/
rm *
touch server.repo

Edit the File server.repo:

[server]
name= My Local Repo
baseurl=file:///var/ftp/pub/Server
enabled=1
gpgcheck=0

Procedure to reset root password if you are using GRUB as a boot loader

Procedure to reset root password if you are using GRUB as a boot loader

1. Select the kernel
2. Press the e key to edit the entry
3. Select second line (the line starting with the word kernel)
4. Press the e key to edit kernel entry so that you can append single user mode
5. Append the letter S (or word Single) to the end of the (kernel) line
6. Press ENTER key
7. Now press the b key to boot the Linux kernel into single user mode
8. At prompt type passwd command to reset password:

Ref: 
http://www.cyberciti.biz/faq/linux-reset-forgotten-root-password/

Recovering Linux Grub Boot Loader Password

If you have, a password protected grub boot loader and you forgot both root and grub password, then you can recover grub-boot loader password using the following method/procedure:

1. Use Knoppix cd
2. Remove the password from Grub configuration file
3. Reboot the system
4. Change the root password

5. Setup new Grub password if required (optional)

Ref:
http://www.cyberciti.biz/tips/howto-recovering-grub-boot-loader-password.html

How to check CRON log in Linux

How to check CRON log in Linux

Step1: Login as root user

Step2: Check that if any cron job exist or not
[oracle@testdb64 ~]#crontab -e
59 23 * * * /home/rman/oracle_backup.sh

Step3: Check the cron log using following command 
[root@testdb64 ~]# tail /var/log/cron
Feb  5 10:30:01 testdb64 crond[17638]: (root) CMD (/usr/lib64/sa/sa1 1 1)
Feb  5 10:40:01 testdb64 crond[18670]: (root) CMD (/usr/lib64/sa/sa1 1 1)
Feb  5 10:50:01 testdb64 crontab[19725]: (oracle) DELETE (oracle)
Feb  5 10:50:01 testdb64 crond[19729]: (root) CMD (/usr/lib64/sa/sa1 1 1)
Feb  5 10:50:04 testdb64 crontab[19734]: (oracle) LIST (oracle)
Feb  5 10:50:37 testdb64 crontab[19785]: (oracle) BEGIN EDIT (oracle)
Feb  5 10:50:44 testdb64 crontab[19785]: (oracle) END EDIT (oracle)
Feb  5 10:51:45 testdb64 crontab[19934]: (oracle) LIST (oracle)
Feb  5 10:52:26 testdb64 crontab[19984]: (oracle) BEGIN EDIT (oracle)
Feb  5 10:52:30 testdb64 crontab[19984]: (oracle) END EDIT (oracle)
[root@testdb64 ~]#

Cron log contains the following information:

Timestamp – The date and time when the cron job was executed
Hostname – The hostname of the server (For example, dev-db)
The cron deamon name and the PID. For example, crond[20399]
Username – The username under which this cron job got executed. For example, john.
CMD – Anything following this is the real command that got executed at that time.

Step by Step Mount USB in Linux

Step by Step Mount USB in Linux

Step1: Check all mount points in this server

[root@oracledbdr1 ~]# fdisk -l
-bash: fdisk: command not found
[root@oracledbdr1 ~]#

--If the above command not found try the following---

Step2: Check all mount points in this server

[root@oracledbdr1 ~]# /sbin/fdisk -l

Disk /dev/sda: 1197.7 GB, 1197759004672 bytes
255 heads, 63 sectors/track, 145619 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          25      200781   83  Linux
/dev/sda2           83017      145619   502858597+  83  Linux
/dev/sda3              26       62491   501758145   83  Linux
/dev/sda4           62492       83016   164867062+   5  Extended
/dev/sda5           62492       72052    76798701   83  Linux
/dev/sda6           72053       78426    51199123+  83  Linux
/dev/sda7           78427       80976    20482843+  83  Linux
/dev/sda8           80977       83016    16386268+  82  Linux swap / Solaris

Partition table entries are not in disk order

Disk /dev/sdb: 2000.3 GB, 2000398934016 bytes
255 heads, 63 sectors/track, 243201 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1               1      243201  1953512001   83  Linux
[root@oracledbdr1 ~]#

Step3: Create a directory to mount the usb

[root@oracledbdr1 ~]# mkdir /mnt/usb


Step4: Mount the usb 

[root@oracledbdr1 ~]# mount /dev/sdb1 /mnt/usb 

Step5: Check the usb mounted or not

[oracle@oracledbdr1 rman_live]$ df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda5              71G  3.3G   65G   5% /
/dev/sda7              19G  6.6G   12G  37% /home
/dev/sda2             465G  206G  236G  47% /back
/dev/sda6              48G  181M   45G   1% /tmp
/dev/sda3             464G  385G   56G  88% /oracledb
/dev/sda1             190M   12M  169M   7% /boot
tmpfs                 7.9G     0  7.9G   0% /dev/shm
/dev/sdb1             1.8T  805G  937G  47% /mnt/usb
[oracle@oracledbdr1 rman_live]$ 

File Permissions Command in Linux

File Permissions Command in Linux

Description:

chmod octal file    -change the permissions of file to octal, which can be found separately for user, group, and world by adding:
● 4 – read (r)
● 2 – write (w)
● 1 – execute (x)

Examples:

chmod 777         -read, write, execute for all
chmod 755         -rwx for owner, rx for group and world For more options, see man chmod.
chown user:group file    -change the owner and group for a file

Allow port in Linux Server

Error : Telnet a port  2001 in 192.168.20.174 server but connection refused

Solution:

1. Check /etc/services location
[root@PhoenixBackup ~]# grep -w 2001 /etc/services
dc              2001/tcp
wizard          2001/udp                        # curry
m3ua            2905/udp                        # De-registered (2001 June 07)
sua             14001/udp                       # De-Registered (2001 June 06)
ATMlen          2001/tcp
[root@PhoenixBackup ~]#

2. If the port exist in /etc/services then allow it into Firewall 

vi /etc/sysconfig/iptables

-A RH-Firewall-1-INPUT -m state --state NEW -m tcp -p tcp --dport 2001 -j ACCEPT

3. Save and close the file. Restart iptables:

# /etc/init.d/iptables restart


Cheers.....