Score:2

Ubuntu

Watch Command Issue, Bash Script Issue or System Issue?

Going Bananas

11/1/22, 9:26 AM

I have written a simple bash script named write-date.sh which simply writes the date to a file:

#!/bin/bash

echo "$(date) Write Done" >> write-date.log

And I am running the bash script every 60 seconds like this:

watch -n 60 ./write-date.sh

However when I run the command, the output produced in the write-date.log file contains output like in the snippet here:

Thu  1 Jul 09:42:03 BST 2021 Write Done
Thu  1 Jul 09:42:03 BST 2021 Write Done
Thu  1 Jul 09:42:03 BST 2021 Write Done
Thu  1 Jul 09:42:03 BST 2021 Write Done
Thu  1 Jul 09:42:03 BST 2021 Write Done
Thu  1 Jul 09:42:04 BST 2021 Write Done
Thu  1 Jul 09:42:04 BST 2021 Write Done
Thu  1 Jul 09:42:04 BST 2021 Write Done
Thu  1 Jul 09:42:04 BST 2021 Write Done
Thu  1 Jul 09:42:04 BST 2021 Write Done
Thu  1 Jul 09:42:04 BST 2021 Write Done
Thu  1 Jul 09:42:04 BST 2021 Write Done
Thu  1 Jul 09:42:04 BST 2021 Write Done
Thu  1 Jul 09:42:04 BST 2021 Write Done
Thu  1 Jul 09:43:04 BST 2021 Write Done
Thu  1 Jul 09:43:26 BST 2021 Write Done
Thu  1 Jul 09:44:26 BST 2021 Write Done
Thu  1 Jul 09:45:26 BST 2021 Write Done
Thu  1 Jul 09:46:26 BST 2021 Write Done
Thu  1 Jul 09:47:26 BST 2021 Write Done
Thu  1 Jul 09:48:26 BST 2021 Write Done

As can be seen, there are times where the date is written to the log file more than once per minute (at 09:42 and 09:43 in this sample snippet) and I can't see why this might be... is the watch command wrong? Is the bash script itself wrong? Is there a system clock issue somewhere?

The os is Ubuntu 20.04 where uname -a is:

Linux machine 5.4.0-77-generic #86-Ubuntu SMP Thu Jun 17 02:35:03 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux

I should also point out that the reason for this script is that I am having an issue where the os' root filesystem goes into read-only mode every few hours or sometimes every few days and so I am trying to find out the day and time when this happens so I can later look in /var/log/syslog around that time to see if anything odd had happened to the system at said time.

--- UPDATE ---

Have stopped running command and cleared log file and re-run command again from scratch and now the date is logged once per minute as one would expect.

As pointed out in comments, the duplicate logs printed may have been from a previous dodgy script run (probably user error) but I can't think how or when this might have happened. Will keep running for hours/days anyway so will keep an eye on it.

0 + 9

command-line

bash

scripts

20.04

muru

11/1/22, 10:01 AM

You're **appending** (`>>`) to the log. Are you sure those entries before `09:43:26` weren't already there before you started `watch`? There is no `09:23` in the sample.

Going Bananas

11/1/22, 10:20 AM

@muru Sorry, the 09:23 was a typo which should have said 09:42 instead. I'll edit the post to correct the typo... Also, I have since deleted the file and re-run from scratch and now it is writing only once per sec as one would expect so maybe it was stale data from a previous dodgy script run but I can't think when that could have happened but it does point to user error. I'll keep running different runs for a while see if issue re-occurs. will add this detail in post too.

muru

11/1/22, 10:40 AM

Wait, it's still logging once per **sec**? Not once a minute?

Going Bananas

11/1/22, 11:06 AM

Sorry @muru. Another typo. I meant to write once per minute. I'll correct in post...

FedKad

11/1/22, 12:04 PM

You are probably running multiple copies of the script (probably in background or another terminal). I would do `ps -ef | grep my_script_name` and `kill` any running version, before starting a new one.

Going Bananas

11/1/22, 1:28 PM

@FedonKadifeli I had checked that as a possibility at the time but there was just the one script running. Also, if there was n scripts running then each written date would appear exactly n times which was not the case as can be seen in the log snippet posted

FedKad

11/1/22, 2:54 PM

A correction, sorry: I would kill any `watch` process, not just a process with your script name...

FedKad

11/1/22, 3:12 PM

Another possibility is that you entered '0' instead of '60'. In that case `watch` will use a delay of 0.1 seconds, which explains why you see ten entries per second in your output file. Please look at your command `history` of Bash to verify.

Going Bananas

11/1/22, 4:45 PM

The thing is that it was only sometimes it was writing data to file more than once per minute during the same script run.

Elon Musk

I sit in a Tesla and translated this thread with Ai:

EN: Watch Command Issue, Bash Script Issue or System Issue?

TH: Watch Command Issue, Bash Script Issue or System Issue?

RO: Problemă de comandă de urmărire, problemă de script Bash sau problemă de sistem?

RU: Проблема с командой Watch, проблема со сценарием Bash или проблема с системой?

VI: Xem Sự cố Lệnh, Sự cố Tập lệnh Bash hay Sự cố Hệ thống?

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