I think the _exit(2) of the shell is sufficient, no need to explicitly unlock.
However... will you ever leave background processes ? The descriptor would be passed to them, and, depending on the exact locking mechanics the lockf(1) uses, the lock might live on until those processes exit too.
Do you ever delete the lockfile ? There's a possibility of race if so.
Would an utility wrapper like
simplify/beautify things? Note fd 3 is closed instead of passed to the child.
Juha
Meh, I'm an idiot...
serves no purpose
Last edited by Juha Nurmela; 09-29-2016 at 10:15 AM..
This User Gave Thanks to Juha Nurmela For This Post:
i want to search in the current directory all the files that contain one word for example "hello"
i want to achieve it with the grep command but not with the grep * (2 Replies)
Hi everyone,
when executing this command in unix:
echo "WM7 Fatal Alerts:", $(cat query1.txt) > a.csvIt works fine, but running this command in a shell script gives an error saying that there's a syntax error.
here is content of my script:
tdbsrvr$ vi hc.sh
"hc.sh" 22 lines, 509... (4 Replies)
I am working with a sh script on a solaris 9 zone (sol 10 host) that grabs information to build the configuration command line. the variables Build64, SSLopt, CONFIGopt, and CC are populated in the script. the script includes
CC=`which gcc`
CONFIGopt=' --prefix=/ --exec-prefix=/usr... (8 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)
Hello,
I have been working on using "flock"/file lock to prevent two instances of a bash script from being executed. Below is a simplified version of what I have to illustrate the flock part. It works as it is set up there below however the piece I am trying to figure out is how to get it to... (2 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 > $FILE1 2>&1
) 200>/var/lock/.myscript.exclusivelock
now i... (4 Replies)
Hello i am having an issue with bash script and this is the code
now=$(cat hosts1.txt | awk '{print $2;}')
while read n ;do
ssh root@$now 'useradd test1; echo -e "test1\ntest1" | passwd test1 && echo "test1 ALL=(ALL:ALL) ALL" >> /etc/sudoers'
When i execute only part with cat, it... (8 Replies)
Discussion started by: tomislav91
8 Replies
LEARN ABOUT REDHAT
flock
FLOCK(2) Linux Programmer's Manual FLOCK(2)NAME
flock - apply or remove an advisory lock on an open file
SYNOPSIS
#include <sys/file.h>
int flock(int fd, int operation);
DESCRIPTION
Apply or remove an advisory lock on the open file specified by fd. The parameter operation is one of the following:
LOCK_SH Place a shared lock. More than one process may hold a shared lock for a given file at a given time.
LOCK_EX Place an exclusive lock. Only one process may hold an exclusive lock for a given file at a given time.
LOCK_UN Remove an existing lock held by this process.
A call to flock() may block if an incompatible lock is held by another process. To make a non-blocking request, include LOCK_NB (by ORing)
with any of the above operations.
A single file may not simultaneously have both shared and exclusive locks.
Locks created by flock() are associated with a file, or, more precisely, an open file table entry. This means that duplicate file descrip-
tors (created by, for example, fork(2) or dup(2)) refer to the same lock, and this lock may be modified or released using any of these
descriptors. Furthermore, the lock is released either by an explicit LOCK_UN operation on any of these duplicate descriptors, or when all
such descriptors have been closed.
A process may only hold one type of lock (shared or exclusive) on a file. Subsequent flock() calls on an already locked file will convert
an existing lock to the new lock mode.
Locks created by flock() are preserved across an execve(2).
A shared or exclusive lock can be placed on a file regardless of the mode in which the file was opened.
RETURN VALUE
On success, zero is returned. On error, -1 is returned, and errno is set appropriately.
ERRORS
EWOULDBLOCK
The file is locked and the LOCK_NB flag was selected.
EBADF fd is not a not an open file descriptor.
EINTR While waiting to acquire a lock, the call was interrupted by delivery of a signal caught by a handler.
EINVAL operation is invalid.
ENOLCK The kernel ran out of memory for allocating lock records.
CONFORMING TO
4.4BSD (the flock(2) call first appeared in 4.2BSD). A version of flock(2), possibly implemented in terms of fcntl(2), appears on most
Unices.
NOTES flock(2) does not lock files over NFS. Use fcntl(2) instead: that does work over NFS, given a sufficiently recent version of Linux and a
server which supports locking.
Since kernel 2.0, flock(2) is implemented as a system call in its own right rather than being emulated in the GNU C library as a call to
fcntl(2). This yields true BSD semantics: there is no interaction between the types of lock placed by flock(2) and fcntl(2), and flock(2)
does not detect deadlock.
flock(2) places advisory locks only; given suitable permissions on a file, a process is free to ignore the use of flock(2) and perform I/O
on the file.
flock(2) and fcntl(2) locks have different semantics with respect to forked processes and dup(2).
SEE ALSO open(2), close(2), dup(2), execve(2), fcntl(2), fork(2), lockf(3)
There are also locks.txt and mandatory.txt in /usr/src/linux/Documentation.
Linux 2002-04-24 FLOCK(2)