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Category :
Database
Resources -> RDBMS Server
DB Version
:
Oracle 8i /
Oracle 9i
OS Details :
Sun Solaris9
If
you had to
deal with the "ORA-27123:
unable to attach to shared memory segment" error then
chances are that you are facing a "sticky bit" problem. This
article is split in to two parts : The first part of this article
gives the technical explanation on what a sticky bit means and in the
second part of the article we will see where oracle uses the Sticky
Bit and also look at ways where we can overcome the errors that
can potentially arise due to missing sticky bit attributes on files.
PART 1:
STICKY BIT one-on-one:
There
are times when an unprivileged user must be able to perform tasks that
require privileges. A good example is the passwd utility which
allows the user to change his or her password but not change the
actual file "/etc/passwd" that stores the password. To find a
way around this problem, UNIX allows for programs with proper
privileges, to change the files even though the user who runs the
program has no "write" or "execute" privileges on the file. A
program that changes its UID is called a SUID program.
When a SUID program is run, its effective UID becomes that of the
owner of the file, rather than of the user who is running it.
If a program is SUID or SGID.
The output of the "ls -al" command will have the x in the
display changed to an s.
CONTENTS PERMISSION MEANING
---s-----
SUID A process that
executes a SUID program has its
effective UID set to be the UID of the programs owner.
-----s--
SGID A process that
executes an SGID program has it
Changed to the programs GID. Files created by the
process can have their primary group set to the GID
as well, depending on the permissions of the
directory.
-rwsr-sr-t
The first s indicates the program is suid
The second s indicates the program is sgid
An Example of how the sticky bit is shown when the ls command is used
on the file:
ls -l /oraclehome/test
-rr-Sr-T 1 oracleuser
dba 24524 Oct 20 2005 /oraclehme/test
PART 2:
One situation where sticky bits
can potentially cause problems are when you copy the oracle software
or the remote login password file to another machine and try to use it
at the new location. Chances are that the sticky bit attributes might
not have been propagated with the copy in which case you might end up
with this error : "ORA-27123:
unable to attach to shared memory segment" when you try to use
the program. If you encounter this error then you'll have to manually
set the sticky bit on the file(s). Let's take the case of the remote
login password file :
With the sticky bit attribute not propagated during a manual copy of
the file: ls -al
orapw -rw-r-----
1 oracle9i dba 3584 Oct 20 2005 orapw
Manually set the sticky bit as
follows: chmod 4640
orapw
After the sticky bit's been
set: ls -al orapw
-rwSr----- 1 oracle9i
dba 3584 Oct 20 2005 orapw
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