I think you did it correctly, and it should have worked.
Using { } instead of ( ) can eventually save a sub-shell. Note that the closing } must be on a new line or preceded by a semicolon.
This User Gave Thanks to MadeInGermany For This Post:
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)
Hi,
We have a lock file being created called lck8c0001 created in Unixware 2.1.2. This is locking a printer.
According to some websites, 8c0001 relates to the device name.
How does one link 8c0001 to those devices listed in the /dev folder?
I have done a ps -lp for all printers and have... (4 Replies)
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)
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)
Hi,
I have a process which can run one instance at a time. Currently we have multiple scripts trying to kickoff this process. I wanted to implement the semaphore mechanism to achieve this.
I was going through few examples. The below code seems to be reasonable solution.
... (5 Replies)
I'm changing my mindset from a few big processes moving data from a few sources under an external, dependency-based scheduler to multiple processes moving data from many sources run by each client cron and possibly interfering with each other. It has the benefits of more granular code but I'm... (11 Replies)
Hi i have a script that check pings and i use flock to so the script wont run
multipul times :
its not the whole script but this is the idea :
(
flock -x -w 3 200 || exit 1
/usr/sbin/fping -c$count -i$interval -a $hosts > $FILE1 2>&1
) 200>/var/lock/.myscript.exclusivelock
now i... (4 Replies)
Discussion started by: batchenr
4 Replies
LEARN ABOUT BSD
flock
FLOCK(2) 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 */
flock(fd, operation)
int fd, 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 the inclusive or of LOCK_SH or LOCK_EX and, possibly, 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
previous 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 VALUE
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.
SEE ALSO open(2), close(2), dup(2), execve(2), fork(2)4.2 Berkeley Distribution May 22, 1986 FLOCK(2)