Creating links is a kind of shortcut to access a file. Links allow more than one file name to refer to the same file.
There are two types of links :
Hard Link
Soft Link or Symbolic links
Hard Link
A hard link is one most power full links in the Linux system when we create a hard link to the file and then delete the file, we can still access the file using the hard link.
[oracle@oracletest scripts]$ ls -l
total 24
-rwxrwxrwx. 1 oracle oracle 42 Oct 21 01:49 ramkumar.txt
-rwxrwxr-x. 1 oracle oracle 1291 Oct 20 23:47 rman_bkp.sh
-rw-rw-r--. 1 oracle oracle 6979 Oct 20 23:48 rman.log
-rwxr--r--. 1 oracle oinstall 515 Sep 9 14:45 setEnv.sh
-rwxr--r--. 1 oracle oinstall 134 Sep 7 10:54 stop_all.sh
[oracle@oracletest scripts]$ ln ramkumar.txt ram
[oracle@oracletest scripts]$ ls -l
total 28
-rwxrwxrwx. 2 oracle oracle 42 Oct 21 01:49 ram
-rwxrwxrwx. 2 oracle oracle 42 Oct 21 01:49 ramkumar.txt
-rwxrwxr-x. 1 oracle oracle 1291 Oct 20 23:47 rman_bkp.sh
-rw-rw-r--. 1 oracle oracle 6979 Oct 20 23:48 rman.log
-rwxr--r--. 1 oracle oinstall 515 Sep 9 14:45 setEnv.sh
-rwxr--r--. 1 oracle oinstall 134 Sep 7 10:54 stop_all.sh
[oracle@oracletest scripts]$ cat ram
HI
Hello
welcome to linux basic commands
[oracle@oracletest scripts]$ rm -rf ramkumar.txt
[oracle@oracletest scripts]$ ls -l
total 24
-rwxrwxrwx. 1 oracle oracle 42 Oct 21 01:49 ram
-rwxrwxr-x. 1 oracle oracle 1291 Oct 20 23:47 rman_bkp.sh
-rw-rw-r--. 1 oracle oracle 6979 Oct 20 23:48 rman.log
-rwxr--r--. 1 oracle oinstall 515 Sep 9 14:45 setEnv.sh
-rwxr--r--. 1 oracle oinstall 134 Sep 7 10:54 stop_all.sh
[oracle@oracletest scripts]$ cat ram
HI Hellowelcome to linux basic commands
Soft Link or Symbolic links
Soft link is another variety type of Linux link, But if we create a soft link of the file and then delete the file, we can’t access the file through the soft link, and the soft link becomes dangling
Syntax: ln -s file_name link_name
Eg: ln -s ramkumar.txt ram
Eg: ls -s sample.txt kar[oracle@oracletest scripts]$ ln -s sample.txt kar
[oracle@oracletest scripts]$ ls -l
total 28
lrwxrwxrwx. 1 oracle oracle 9 Oct 21 23:12 ram -> sample.txt-rw-rw-r--. 1 oracle oracle 49 Oct 21 23:12 ramkumar.txt
-rwxrwxrwx. 1 oracle oracle 42 Oct 21 01:49 ram
-rwxrwxr-x. 1 oracle oracle 1291 Oct 20 23:47 rman_bkp.sh
-rw-rw-r--. 1 oracle oracle 6979 Oct 20 23:48 rman.log
-rwxr--r--. 1 oracle oinstall 515 Sep 9 14:45 setEnv.sh
-rwxr--r--. 1 oracle oinstall 134 Sep 7 10:54 stop_all.sh
[oracle@oracletest scripts]$ cat ram
Good morning
How are you all
Take care
Bye Bye !
[oracle@oracletest scripts]$ rm -rf sample.txt
[oracle@oracletest scripts]$ ls -l
total 24
lrwxrwxrwx. 1 oracle oracle 9 Oct 21 23:12 ram -> sample.txt
-rwxrwxrwx. 1 oracle oracle 42 Oct 21 01:49 ram
-rwxrwxr-x. 1 oracle oracle 1291 Oct 20 23:47 rman_bkp.sh
-rw-rw-r--. 1 oracle oracle 6979 Oct 20 23:48 rman.log
-rwxr--r--. 1 oracle oinstall 515 Sep 9 14:45 setEnv.sh
-rwxr--r--. 1 oracle oinstall 134 Sep 7 10:54 stop_all.sh
[oracle@oracletest scripts]$ cat ram
cat: ram: No such file or directory
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locate command and find command is used to search a file by name. But, the difference between both commands is that locating command is a background process and searches the file in the database whereas, find command searches in the file system. The locate command is much faster than the find command.
We have some options in locating search commands by locate -h (help cmd) Search for entries in a locate database.
-A, --all only print entries that match all patterns
-b, --basename match only the base name of path names
-c, --count only print number of found entries
-d, --database DBPATH use DBPATH instead of default database (which is
/var/lib/mlocate/mlocate.db)
-e, --existing only print entries for currently existing files
-L, --follow follow trailing symbolic links when checking file
existence (default)
-h, --help print this help
-i, --ignore-case ignore case distinctions when matching patterns
-l, --limit, -n LIMIT limit output (or counting) to LIMIT entries
-m, --mmap ignored, for backward compatibility
-P, --nofollow, -H don't follow trailing symbolic links when checking file
existence
-0, --null separate entries with NUL on output
-S, --statistics don't search for entries, print statistics about each
used database
-q, --quiet report no error messages about reading databases
-r, --regexp REGEXP search for basic regexp REGEXP instead of patterns
--regex patterns are extended regexps
-s, --stdio ignored, for backward compatibility
-V, --version print version information
-w, --wholename match whole path name (default)
find command is one of the most powerful tools in Linux, It supports searching by file, folder, name, creation date, modification date, owner, and permissions.
By using the ‘-exec’
Syntax: find [where to start searching from]
[expression determines what to find] [-options] [what to find]
Eg: find ramkumar
Options :
-exec CMD: The file being searched which meets the above criteria and returns 0
for as its exit status for successful command execution.
-ok CMD : It works same as -exec except the user is prompted first.
-inum N : Search for files with inode number ‘N’.
-links N : Search for files with ‘N’ links.
-name demo : Search for files that are specified by ‘demo’.
-newer file : Search for files that were modified/created after ‘file’.
-perm octal : Search for the file if permission is ‘octal’.
-print : Display the path name of the files found by using the rest of the criteria.
-empty : Search for empty files and directories.
-size +N/-N : Search for files of ‘N’ blocks; ‘N’ followed by ‘c’can be used to
measure size in characters; ‘+N’ means size > ‘N’ blocks and ‘-N’ means
size < 'N' blocks.
-user name : Search for files owned by user name or ID ‘name’.
\(expr \) : True if ‘expr’ is true; used for grouping criteria combined with OR or AND.
! expr : True if ‘expr’ is false.
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Every file and directory in your Linux system has the following 3 permissions defined for all the 3 owners discussed above.
Read: This permission give you the authority to open and read a file.
Write: The write permission on a directory gives you the authority to add, remove and rename files stored in the directory
Execute: In Windows, an executable program usually has an extension “.exe” and which you can easily run. Linux, you cannot run a program unless the execute permission is set. If the execute permission is not set, you might still be able to see/modify the program code(provided read & write permissions are set), but not run it.
Let’s see file permissions in Linux with examples:
ls – l This list command will show the file permissions
[oracle@oracletest scripts]$ ls -l
total 24
-rw-rw-r--. 1 oracle oracle 42 Oct 21 01:49 kiruba.txt
-rwxrwxr-x. 1 oracle oracle 1291 Oct 20 23:47 rman_bkp.sh
-rw-rw-r--. 1 oracle oracle 6979 Oct 20 23:48 rman.log
-rwxr--r--. 1 oracle oinstall 515 Sep 9 14:45 setEnv.sh
-rwxr--r--.1 oracle oinstall 134 Sep 7 10:54 stop_all.sh
So, Here we listed some files with permissions
r = read permission w = write permission x = execute permission – = no permission
permissions with chmod command
We can use the chmod command which stands for change mode. Using the command, we can set permissions (read, write, execute) on a file/directory for the owner, group.
There are 2 ways to use the command
Absolute mode
Symbolic mode
Absolute(Numeric) Mode
In this mode file permissions are not represented as characters, we can give in a three-digit octal number.
Number
Permission Type
Symbol
0
No Permission
—
1
Execute
–x
2
Write
-w-
3
Execute + Write
-wx
4
Read
r–
5
Read + Execute
r-x
6
Read +Write
rw-
7
Read + Write +Execute
rwx
Example: chmod three-digit octal number filename
chmod 777 kiruba.txt
we were given this permission to text file we can able to read, write and execute the specified file
Symbolic Mode
In the Absolute mode, we can change permissions for all 3 owners. In the symbolic mode, we can modify the permissions of a specific owner also make use of mathematical symbols to modify the Linux file permissions.
Operator
Description
+
Adds permission to a file or directory
–
Removes the permission
=
Sets the permission and overrides the permissions set earlier.
The various owners are represented as –
User Denotations
u
user/owner
g
group
o
other
a
all
Changing Ownership and Group:
changing the ownership of a file/directory we can use the following command
chown user filename
Eg: chown kiruba rman_backup.log
OLD DISKGROUP NAME: DATA NEW DISKGROUP NAME: ORA_DATA
[oracle@oracleagent:+ASM] sqlplus / as sysasm
SQL*Plus: Release 19.0.0.0.0 – Production on Wed Oct 20 16:38:25 2021
Version 19.12.0.0.0
Copyright (c) 1982, 2021, Oracle. All rights reserved.
Connected to:
Oracle Database 19c Enterprise Edition Release 19.0.0.0.0 – Production
Version 19.12.0.0.0
SYS@+ASM> alter diskgroup DATA dismount;
alter diskgroup DATA dismount
*
ERROR at line 1:
ORA-15032: not all alterations performed
ORA-15027: active use of diskgroup “DATA” precludes its dismount
SYS@+ASM> alter diskgroup DATA dismount force;
Diskgroup altered.
SYS@+ASM> exit
Disconnected from Oracle Database 19c Enterprise Edition Release 19.0.0.0.0 – Production
Version 19.12.0.0.0
[oracle@oracleagent:+ASM] renamedg dgname=DATA newdgname=ORA_DATA verbose=true
Parameters in effect:
Old DG name : DATA
New DG name : ORA_DATA
Phases :
Phase 1
Phase 2
Discovery str : (null)
Clean : TRUE
Raw only : TRUE
renamedg operation: dgname=DATA newdgname=ORA_DATA verbose=true
Executing phase 1
Discovering the group
Performing discovery with string:
Identified disk ASM:ASM Library – Generic Linux, version 2.0.12 (KABI_V2):ORCL:ORA_DATA_0001 with disk number:0 and timestamp (33120742 632048640)
Checking for hearbeat…
Re-discovering the group
Performing discovery with string:
Identified disk ASM:ASM Library – Generic Linux, version 2.0.12 (KABI_V2):ORCL:ORA_DATA_0001 with disk number:0 and timestamp (33120742 632048640)
Checking if the diskgroup is mounted or used by CSS
Checking disk number:0
Generating configuration file..
Completed phase 1
Executing phase 2
Looking for ORCL:ORA_DATA_0001
Modifying the header
Completed phase 2
[oracle@oracleagent:+ASM] sqlplus / as sysasm
SQL*Plus: Release 19.0.0.0.0 – Production on Wed Oct 20 16:41:16 2021
Version 19.12.0.0.0
Copyright (c) 1982, 2021, Oracle. All rights reserved.
Connected to:
Oracle Database 19c Enterprise Edition Release 19.0.0.0.0 – Production
Version 19.12.0.0.0
SYS@+ASM> alter diskgroup ORA_DATA mount force;
Diskgroup altered.
SYS@+ASM> exit
Disconnected from Oracle Database 19c Enterprise Edition Release 19.0.0.0.0 – Production
Version 19.12.0.0.0
[oracle@oracleagent:+ASM] ps -ef | grep pmon
oracle 1547 1 0 Aug18 ? 00:02:44 asm_pmon_+ASM
[oracle@oracleagent:+ASM] asmcmd
ASMCMD> lsdg
State Type Rebal Sector Logical_Sector Block AU Total_MB Free_MB Req_mir_free_MB Usable_file_MB Offline_disks Voting_files Name
MOUNTED EXTERN N 512 512 4096 4194304 511996 511896 0 511896 0 N ORA_DATA/
ASMCMD>
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SQL> select name from v$tablespace;
NAME
------------------------------
SYSAUX
SYSTEM
UNDOTBS1
USERS
TEMP
TEST
6 rows selected.
SQL> alter tablespace users offline;
Tablespace altered.
SQL> exit
[oratest@oracle dbs]$ date
Wed Sep 8 22:15:37 IST 2021
Connect RMAN and backup tablespace
[oratest@oracle dbs]$ rman target/
Recovery Manager: Release 19.0.0.0.0 - Production on Wed Sep 8 22:16:02 2021
Version 19.3.0.0.0
Copyright (c) 1982, 2019, Oracle and/or its affiliates. All rights reserved.
connected to target database: TEST (DBID=2378581000)
RMAN> restore tablespace users until time "to_date ('08-SEP-2021 22:15:37','DD-MON-YYYY:HH24:MI:SS')";
Starting restore at 08-SEP-21
using target database control file instead of recovery catalog
allocated channel: ORA_DISK_1
channel ORA_DISK_1: SID=66 device type=DISK
channel ORA_DISK_1: starting datafile backup set restore
channel ORA_DISK_1: specifying datafile(s) to restore from backup set
channel ORA_DISK_1: restoring datafile 00007 to /u01/app/oracle/oradata/TEST/users01.dbf
channel ORA_DISK_1: reading from backup piece /u01/app/oracle/oradata/TEST/backup/1408j583_1_1
channel ORA_DISK_1: piece handle= /u01/app/oracle/oradata/TEST/backup/1408j583_1_1 tag=TAG20210908T221323
channel ORA_DISK_1: restored backup piece 1
channel ORA_DISK_1: restore complete, elapsed time: 00:00:01
Finished restore at 08-SEP-21
[oracle@oracle ~]$ rman target/
RMAN> restore tablespace users;
Starting restore at 08-SEP-21
using channel ORA_DISK_1
skipping datafile 5; already restored to file /u01/app/oracle/oradata/TEST/datafile/users.dbf
restore not done; all files read only, offline, excluded, or already restored
Finished restore at 08-SEP-21
RMAN> recover tablespace users;
Starting recover at 08-SEP-21
using channel ORA_DISK_1
starting media recovery
archived log for thread 1 with sequence 32 is already on disk as file /u01/app/oracle/fast_recovery_area/TEST/archivelog/2021_09_02/o1_mf_1_32_jlzwlxjb_.arc
media recovery complete, elapsed time: 00:00:12
Finished recover at 08-SEP-21
RMAN> exit
Recovery Manager complete.
[oratest@oracle ~]$ sqlplus / as sysdba
SQL*Plus: Release 19.0.0.0.0 - Production on Wed Sep 8 22:51:07 2021
Version 19.3.0.0.0
Copyright (c) 1982, 2019, Oracle. All rights reserved.
Connected to:
Oracle Database 19c Enterprise Edition Release 19.0.0.0.0 - Production
Version 19.3.0.0.0
SQL> select name from v$datafile;
NAME
--------------------------------------------------------------------------------
/u01/app/oracle/oradata/TEST/system01.dbf
/u01/app/oracle/oradata/TEST/test03.dbf
/u01/app/oracle/oradata/TEST/sysaux01.dbf
/u01/app/oracle/oradata/TEST/undotbs01.dbf
/u01/app/oracle/oradata/TEST/test01.dbf
/u01/app/oracle/oradata/TEST/users01.dbf
6 rows selected.
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[oratest@oracle ~]$ export ORACLE_SID=test
[oratest@oracle ~]$ sqlplus / as sysdba
SQL*Plus: Release 19.0.0.0.0 - Production on Wed Sep 8 21:25:19 2021
Version 19.3.0.0.0
Copyright (c) 1982, 2019, Oracle. All rights reserved.
Connected to:
Oracle Database 19c Enterprise Edition Release 19.0.0.0.0 - Production
Version 19.3.0.0.0
SQL> show parameter pfile;
NAME TYPE VALUE
------- ------- ------------------------------
spfile string /u01/app/oracle/product/19.0.0
/dbhome_1/dbs/spfiletest.ora
Connect RMAN and Backup the Spfile:
[oratest@oracle ~]$ rman target /
Recovery Manager: Release 19.0.0.0.0 - Production on Wed Sep 8 21:26:38 2021
Version 19.3.0.0.0
Copyright (c) 1982, 2019, Oracle and/or its affiliates. All rights reserved.
connected to target database: TEST (DBID=2378581000)
RMAN> backup spfile;
Starting backup at 08-SEP-21
using target database control file instead of recovery catalog
allocated channel: ORA_DISK_1
channel ORA_DISK_1: SID=66 device type=DISK
channel ORA_DISK_1: starting full datafile backup set
channel ORA_DISK_1: specifying datafile(s) in backup set
including current SPFILE in backup set
channel ORA_DISK_1: starting piece 1 at 08-SEP-21
channel ORA_DISK_1: finished piece 1 at 08-SEP-21
piece handle=/u01/app/oracle/oradata/TEST/backup/1208j2hb_1_1 tag=TAG20210908T212707 comment=NONE
channel ORA_DISK_1: backup set complete, elapsed time: 00:00:01
Finished backup at 08-SEP-21
Starting Control File and SPFILE Autobackup at 08-SEP-21
piece handle=/u01/app/oracle/oradata/TEST/backup/c-2378581000-20210908-00 comment=NONE
Finished Control File and SPFILE Autobackup at 08-SEP-21
sqlplus / as sysdba
SQL*Plus: Release 19.0.0.0.0 - Production on Wed Sep 8 21:28:32 2021
Version 19.3.0.0.0
Copyright (c) 1982, 2019, Oracle. All rights reserved.
Connected to:
Oracle Database 19c Enterprise Edition Release 19.0.0.0.0 - Production
Version 19.3.0.0.0
SQL> shut immediate
Database closed.
Database dismounted.
ORACLE instance shut down.
Move the Spfile to Backup File
[oracle@oracle ~]$ cd $ORACLE_HOME/dbs
[oracle@oracle dbs]$ ls
Spfiletest.ora inittest.ora
[oracle@oracle dbs]$ mv spfiletest.ora spfiletest.ora_bkp
[oracle@oracle dbs]$ ls
initorcl.ora Spfiletest.ora_bkp
[oratest@oracle dbs]$ rman target/
Recovery Manager: Release 19.0.0.0.0 - Production on Wed Sep 8 21:33:14 2021
Version 19.3.0.0.0
Copyright (c) 1982, 2019, Oracle and/or its affiliates. All rights reserved.
connected to target database (not started)
RMAN> set dbid 2378581000
executing command: SET DBID
start the database in force option with nomount stage
RMAN> startup force nomount;
Oracle instance started
Total System Global Area 1543500144 bytes
Fixed Size 8896880 bytes
Variable Size 905969664 bytes
Database Buffers 620756992 bytes
Redo Buffers 7876608 bytes
Restore the spfile from Auto backup Location
RMAN> restore spfile from autobackup;
Starting restore at 08-SEP-21
using target database control file instead of recovery catalog
allocated channel: ORA_DISK_1
channel ORA_DISK_1: SID=38 device type=DISK
recovery area destination: /u01/app/oracle/fast_recovery_area
database name (or database unique name) used for search: TEST
channel ORA_DISK_1: AUTOBACKUP /u01/app/oracle/fast_recovery_area/TEST/autobackup/2021_09_05/o1_mf_s_1082499783_jm9xhjjd_.bkp found in the recovery area
channel ORA_DISK_1: looking for AUTOBACKUP on day: 20210905
channel ORA_DISK_1: restoring spfile from AUTOBACKUP /u01/app/oracle/fast_recovery_area/TEST/autobackup/2021_09_05/o1_mf_s_1082499783_jm9xhjjd_.bkp
channel ORA_DISK_1: SPFILE restore from AUTOBACKUP complete
Finished restore at 08-SEP-21
Recovery Manager complete.
[oracle@oracle ~]$ sqlplus / as sysdba
SQL*Plus: Release 19.0.0.0.0 - Production on Sun Sep 5 22:32:18 2021
Version 19.3.0.0.0
Copyright (c) 1982, 2019, Oracle. All rights reserved.
Connected to:
Oracle Database 19c Enterprise Edition Release 19.0.0.0.0 - Production
Version 19.3.0.0.0
SQL> select name,open_mode from v$database;
NAME OPEN_MODE
--------- --------------------
TEST MOUNTED
Using alter command open the database
SQL> alter database open;
Database altered.
SQL> select name,open_mode from v$database;
NAME OPEN_MODE
--------- --------------------
TEST READ WRITE
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