06-24-2009
Applying lock on a file in Unix Ksh
Hi,
How can we apply lock on a text file through Unix Ksh script. I did found a command flock (file descriptor) but am not very acquainted with the usage.
Can anybody tell me if I need to use Flock command for applying locks to a file while writing on it. If the person can explain the usage with an example, that will be really great.
If this is not the right command, can anyone let me know what command shall i use.
10 More Discussions You Might Find Interesting
1. UNIX for Dummies Questions & Answers
We wish to keep a sequence number in a file. When someone wants to get the next sequence number we need to lock the file, get the next number and increment it by one. How do you do that?
I know how to get the number and increment it but how do I lock the file and test that it is locked or not... (1 Reply)
Discussion started by: tammy_schmuki
1 Replies
2. Red Hat
Hello all,
If anyone has time, I have a few questions:
How do I do the following in Linux. We are using Red Hat and Oracle Enterprise Linux, which is based on Red Hat too.
1. How to lock the account after a few (like 3) invalid password attempts?
2. How do you lock a screen after 30... (1 Reply)
Discussion started by: nstarz
1 Replies
3. UNIX for Dummies Questions & Answers
Hi,
I have a ksh shell script that accesses databases to drop and create tables and the script also creates text files.
This shell script is accessed thru a java application that i would like to turn multi-user, but the only way that i can do that is if I can figure out a way to lock the shell... (2 Replies)
Discussion started by: ndedhia1
2 Replies
4. UNIX for Advanced & Expert Users
Hi all,
I have to test some user priviliges. The goal is to be sure that an unauthorized user can't restart some modules (ssh, mysql etc...).
I'm trying to automate it with a shell script but in same cases I got the syslog broadcast message.
Is there any way to simply get a return code... (3 Replies)
Discussion started by: Dedalus
3 Replies
5. UNIX for Dummies Questions & Answers
Hi,
I'm having a general query. If we do cat <file name> on a Ebcidic format file then many unknown characters are displayed in my screen.
Can we change the character set related to EBCIDIC in session level and apply the cat command on a EBCIDIC file? By doing so can we able to see the... (2 Replies)
Discussion started by: poova
2 Replies
6. UNIX for Dummies Questions & Answers
Dear all,
I know this might be a simple and silly question but I am struggling with it
I have a long unix script and in a section of if I want to use a python script which should select all the files and run the script on it (as a whole)
the loop I have is selecting file by file and I dont know... (2 Replies)
Discussion started by: A-V
2 Replies
7. Ubuntu
I wrote two shell scripts in UNIX that renames the same file and scheduled them at the same time.
The following are the steps that I followed:-
1. I wrote 2 scripts named s1.sh and s2.sh, both trying to add “exec_” prefix to the name of the files present in a folder i which already don't start... (4 Replies)
Discussion started by: piuli
4 Replies
8. Shell Programming and Scripting
Hi Forum.
I have the following challenge at work that I need to write a script for.
I have a file abc.txt with the following contents:
4560123456
4570987654
4580654321
I want to be able to search/replace in abc.txt - the first 4 characters anything starting with 4560 to 7777; 4570... (3 Replies)
Discussion started by: pchang
3 Replies
9. Shell Programming and Scripting
I am trying to apply an awk action over multiple files in a directory. It is a simple action, I want to print out the 1st 2 columns (i.e. $1 and $2) in each tab-separated document and output the result in a new file *.pp
This is the awk that I have come up with so far, which is not giving me a... (6 Replies)
Discussion started by: owwow14
6 Replies
10. Shell Programming and Scripting
Hello Team-
we would like to implement an approach which has to write the log file simultaneously
when .sql file is executing by Unix process. At present,it is writing the log file
once the process is completed. I've tested the current process with the below
approaches and none of them... (1 Reply)
Discussion started by: Hima_B
1 Replies
LEARN ABOUT OPENDARWIN
flock
FLOCK(2) BSD System Calls Manual FLOCK(2)
NAME
flock -- apply or remove an advisory lock on an open file
SYNOPSIS
#include <sys/file.h>
#define LOCK_SH 1 /* shared lock */
#define LOCK_EX 2 /* exclusive lock */
#define LOCK_NB 4 /* don't block when locking */
#define LOCK_UN 8 /* unlock */
int
flock(int fd, int operation);
DESCRIPTION
Flock() applies or removes an advisory lock on the file associated with the file descriptor fd. A lock is applied by specifying an operation
parameter that is one of LOCK_SH or LOCK_EX with the optional addition of LOCK_NB. To unlock an existing lock operation should be LOCK_UN.
Advisory locks allow cooperating processes to perform consistent operations on files, but do not guarantee consistency (i.e., processes may
still access files without using advisory locks possibly resulting in inconsistencies).
The locking mechanism allows two types of locks: shared locks and exclusive locks. At any time multiple shared locks may be applied to a
file, but at no time are multiple exclusive, or both shared and exclusive, locks allowed simultaneously on a file.
A shared lock may be upgraded to an exclusive lock, and vice versa, simply by specifying the appropriate lock type; this results in the pre-
vious lock being released and the new lock applied (possibly after other processes have gained and released the lock).
Requesting a lock on an object that is already locked normally causes the caller to be blocked until the lock may be acquired. If LOCK_NB is
included in operation, then this will not happen; instead the call will fail and the error EWOULDBLOCK will be returned.
NOTES
Locks are on files, not file descriptors. That is, file descriptors duplicated through dup(2) or fork(2) do not result in multiple instances
of a lock, but rather multiple references to a single lock. If a process holding a lock on a file forks and the child explicitly unlocks the
file, the parent will lose its lock.
Processes blocked awaiting a lock may be awakened by signals.
RETURN VALUES
Zero is returned if the operation was successful; on an error a -1 is returned and an error code is left in the global location errno.
ERRORS
The flock() call fails if:
[EWOULDBLOCK] The file is locked and the LOCK_NB option was specified.
[EBADF] The argument fd is an invalid descriptor.
[EINVAL] The argument fd refers to an object other than a file.
[EOPNOTSUPP] The referenced descriptor is not of the correct type.
SEE ALSO
open(2), close(2), dup(2), execve(2), fork(2)
HISTORY
The flock() function call appeared in 4.2BSD.
4.2 Berkeley Distribution December 11, 1993 4.2 Berkeley Distribution