How to lock a file in unix?

Thread Tools Search this Thread
Top Forums UNIX for Dummies Questions & Answers How to lock a file in unix?
# 1  
Old 05-25-2001

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 locked.
x=`cat filewithseq`
echo $x > filewithseq
Someone must be doing this already. I know that printer job numbers work in a similar way.
# 2  
Old 05-25-2001
In this situation, people usually create a test condition before opening the file and operating on the sequence number. The normal test condition is the existance of a temporary file i.e. yourprogramname.LOCK.

Before a script or command opens the file, it first tests for the existance of the LOCK file. If the file exists, the process terminates. How it terminates depends on the user requirements.

That is how it is normally done with scripts. If you need a more atomic method, you must use system calls closer to the kernel and this will require C (or some other) programming wrapper.
Login or Register to Ask a Question

Previous Thread | Next Thread

10 More Discussions You Might Find Interesting

1. Ubuntu

How to lock a file through UNIX KSH shell script?

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 and, 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

2. Shell Programming and Scripting

How to lock Oracle table through UNIX?

Hi frndz, Can anyone provide me some input or pseudo code for my req as mentioned below... I am loading 2 files through unix script into oracle i am doing some updates also i am getting an error where both files try to update the table simultaneously and my script fails.. so i... (3 Replies)
Discussion started by: gnnsprapa
3 Replies

3. UNIX for Advanced & Expert Users

Testing privileges -lock lockfile /var/lock/subsys/..- Permission denied

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

4. Red Hat

Security Question: Lock after invalid login, Session Lock and Required Minimum Password Length

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

5. UNIX for Advanced & Expert Users

file lock

I have an Essbase installation on Solaris 10 and need to get the backups configured. Unfortunately several key files are locked and Essbase (OLAP application) is not releasing the locks when the Essbase or the applications within stop running. It appears I can use chmod to unlock the files but I... (0 Replies)
Discussion started by: JavaBrian
0 Replies

6. Shell Programming and Scripting

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... (3 Replies)
Discussion started by: kum5256
3 Replies

7. Shell Programming and Scripting

How to lock an inbox using UNIX scripting

Hi All, I have an inbox , which recieves mails every second. I need to copy the contents of the mails in the inbox to a file , say once every minute. Then clear the content of the inbox. There is a possibility that a new mail might come in before I delete the content. Please let me know if... (1 Reply)
Discussion started by: Manju-he202
1 Replies

8. Shell Programming and Scripting

Folder Lock in Unix

I am a new user of linux. I have 2 Queries 1) I recently started working with shell script, and now i plan to make a folder lock using a shell script. I have ubuntu 8.04 installed on my system. 2) When i searched on this forum all i got was mini-httpd, and apache2-utils package, but they... (2 Replies)
Discussion started by: tsunami
2 Replies

9. UNIX for Dummies Questions & Answers

how to lock keyboard without using lock command

how can I lock my keyboard while I'm away from the computer without using lock command. What other commands gives me the option to lock keyboard device? thanks (7 Replies)
Discussion started by: dianayun
7 Replies

10. UNIX for Dummies Questions & Answers

lock file!

I found a lock file like this lrwxrwxr-x 1 sskb apollo 16 Oct 22 22:00 lock -> hostname:2747 (pl. note that hostname is a number like but this was not shown in the file manager eventhough I had selected to show the hidden files. I could not even read the... (4 Replies)
Discussion started by: sskb
4 Replies
Login or Register to Ask a Question