bash dropping SIGHUPs Post: 302548477

Sponsored Content

Top Forums Shell Programming and Scripting bash dropping SIGHUPs Post 302548477 by Corona688 on Thursday 18th of August 2011 01:18:56 PM

08-18-2011

Registered User

I don't think it's ever going to miss a HUP, it will still set the variable. The loop may just detect it 30 seconds late.

There's no point backgrounding sleep 30 when all you're going to do is wait for it. You catch the circumstance when HUP comes in the instant between running wait and waiting for wait, and open 3 other circumstances where the HUP could creep in before you're ready.

A C application would use SIGMASK to temporarily stop a signal but shell doesn't have this... hmm...

How about a pipe?

Code:

#!/bin/sh

trap "rm -f /tmp/$$" HUP

echo "pid is $$"
exec 5>&2               # Save stderr
exec  2> /dev/null      # stop error spew

while true
do
        mkfifo /tmp/$$  # Recreate FIFO

        # wait for fifo to be deleted, which will make read fail
        while read X < /tmp/$$ ; do true ; done

        echo "read loop broken"
done

exec 2>&5       # restore stderr
exec 5>&-       # close fd 5

The shell will create a FIFO and try to read from it. Since there's no other process writing to it, it will block until something does something to it. A HUP signal will delete the FIFO, causing the read to fail. Once it's ready, the shell will create a new FIFO and start over.

Redirecting stderr is necessary since deleting the FIFO causes a bit of error spam. You can redirect into >&5 if you need to write to stderr.

Tested this in lots of shells and two OSes so it looks decently portable.

Last edited by Corona688; 08-18-2011 at 02:24 PM..

Corona688

View Public Profile for Corona688

Visit Corona688's homepage!

Find all posts by Corona688

10 More Discussions You Might Find Interesting

1. UNIX for Advanced & Expert Users

strintercept dropping message on unixware

i have unixware 2.1. A warning message Strintercept dropping message start scrolling on screen. does anyone have any idea what it means? :confused: and some times system hangs with all terminals.?

2. Shell Programming and Scripting

Sed command dropping last record in File

Hello: I wrote a sed statement that is inserting 3 variables at the beginning of each record in a comma-delimited file: for FILE in *gnrc_lkup.csv do c=`echo $FILE | cut -c1-3` d=`grep $c $RTLIST | cut -c4-6` e=`grep $c $RTLIST | cut -c7` f=`grep $c $RTLIST | cut -c8` sed -e...

3. Linux

Free Linux Memory by Dropping Caches

Linux Kernels 2.6.16 and up provide a way to instruct the kernel to drop the page cache, inode and dentry caches on command. This tip can help free Linux memory without a reboot. Note: This is a non-destructive operation. Dirty objects are not freeable, hence; you must run sync beforehand. ...

4. Shell Programming and Scripting

Dropping Records for unknown reason in awk script

Hi, I have written the following it is pretty sloppy but I don't see any reason why I should be losing 54 records from a 3.5 million line file after using it. What I am doing: I have a 3.5 million record file with about 80,000 records need a correction. They are missing the last data from...

5. Red Hat

Download speed gradually dropping

RH 4.2.1.13 Hi All, I just installed RH and I am able to connect to the internet via my router. My high speed is such that I should be able to download at over 1000 kb/s. While trying to download oracle database, it is starting at above 1000kb/s and gradually droping to below 40kb/s which...

6. Solaris

Names dropping out of /etc/aliases

We are having a problem with names being dropped from the /etc/mail/aliases file. There's no pattern to the names being dropped. It is very random. We are running sendmail 8.14.3 on a Solaris 10 server. There are about 9000 lines in the /etc/mail/aliases file. Is there a limitation on...

7. Emergency UNIX and Linux Support

Dropping Connection

Hi folks, We are pushing messages to an IBM MQ queue on a AIX server where our client connects to from their Windows server and pick up the message. The problem is that every now and then the connection drops and the client application cannot pick up the message. Someone has to bring up the...

8. Red Hat

Create same file name to directory name without dropping it

Hi, Under '/home' directory, there is one file called 'maddy'.Usually there used to be directories under /home directory. # ls -alrt total 132 drwx------ 2 hcladmin sys 4096 May 30 10:54 admin drwxr-xr-x 29 root root 4096 Aug 27 03:54 .. drwx------ 2 v6admin dba ...

9. Solaris

PF refreshes dropping user connections

We often have to update our ipfilter rules on Solaris 11. svcadm refresh ipfilter drops users every time (we're logged in via the global and then a zlogin to the zone in question). Is there any way not to drop user's connections when modifying ipfilter rules and refreshing the service?

10. UNIX for Beginners Questions & Answers

Pc's dropping connection to NFS

Hi there. I have a problem with pc's dropping their mounts to a network Nas. The Nas is a Synology DiskStation, it has enough concurrent connections which I think off the top of my head is about 200 and I only need 120. So, question 1 is why will a unix box drop a mount, and 2, how can I...

LEARN ABOUT OPENSOLARIS

libbash

LIBBASH(7)							  libbash Manual							LIBBASH(7)

NAME

     libbash -- A bash shared libraries package.

DESCRIPTION

     libbash  is  a package that enables bash dynamic-like shared libraries. Actually its a tool for managing bash scripts whose functions you may
     want to load and use in scripts of your own.

     It contains a 'dynamic loader' for the shared libraries ( ldbash(1)), a configuration tool (ldbashconfig(8)), and some libraries.

     Using ldbash(1) you are able to load loadable bash libraries, such as getopts(1) and hashstash(1).  A bash shared library that can be  loaded
     using
     ldbash(1) must answer 4 requirments:

     1.     It must be installed in $LIBBASH_PREFIX/lib/bash (default is /usr/lib/bash).

     2.     It must contain a line that begins with '#EXPORT='.  That line will contain (after the '=') a list of functions that the library
	    exports.  I.e. all the function that will be usable after loading that library will be listed in that line.

     3.     It must contain a line that begins with '#REQUIRE='.  That line will contain (after the '=') a list of bash libraries that are
	    required for our library.  I.e. every bash library that is in use in our bash library must be listed there.

     4.     The library must be listed (For more information, see ldbashconfig(8)).

   Basic guidelines for writing library of your own:
     1.     Be aware, that your library will be actually sourced. So, basically, it should contain (i.e define) only functions.

     2.     Try to declare all variables intended for internal use as local.

     3.     Global variables and functions that are intended for internal use (i.e are not defined in '#EXPORT=') should begin with:
		  __<library_name>_
	    For example, internal function myfoosort of hashstash library should be named as
		  __hashstash_myfoosort
	    This helps to avoid conflicts in global name space when using libraries that come from different vendors.

     4.     See html manual for full version of this guide.

AUTHORS

     Hai Zaar <haizaar@haizaar.com>
     Gil Ran <ril@ran4.net>

SEE ALSO

     ldbash(1), ldbashconfig(8), getopts(1), hashstash(1) colors(1) messages(1) urlcoding(1) locks(1)

Linux								       Epoch								     Linux

10 More Discussions You Might Find Interesting

1. UNIX for Advanced & Expert Users

strintercept dropping message on unixware

Discussion started by: kapilverma_udr

2. Shell Programming and Scripting

Sed command dropping last record in File

Discussion started by: bheeke

3. Linux

Free Linux Memory by Dropping Caches

Discussion started by: Neo

4. Shell Programming and Scripting

Dropping Records for unknown reason in awk script

Discussion started by: mkastin