When I schedule a job with 'at' it is assigned an id, viz:
job 44 at 2014-01-28 17:30
When that job runs I would like to get at that id from within it. This is on Centos, FWIW. I have established that no environment variable contains the ID. When the Perl code in that job runs I would like it to be able to print the job ID (44 in this example).
Yes, I know that atq shows an = next to jobs that are executing, but there might be more than one of those at a time.
I could do something like pass a unique argument to the job when scheduling it, capture the ID, save that and the argument to a file somewhere, read that from the job. That's a lot of work I'd rather not go to if I don't have to, and it seems like this should be simple but I'm drawing a blank.
What follows is figured out by reading sources of at-3.14. The way at puts job id and the time when it is run into the file name should be similar for any version, but I haven't checked this.
To begin whith at encodes the job id and the time when a particular job should be run into the file name describing a job. The file name has format aJJJJJTTTTTTTT, where JJJJJ is 5 character hexadecimal string, the job id, and TTTTTTTT is an 8 character hexadecimal string, the time when the job should be run. The time is stored as seconds from the epoch.
At jobs are run by feeding a job description file as the standard input to sh -c. Fortunately the Linux kernel provides a symbolic link, /proc/self/fd/0, which will point to the standard input of the process currently being executed (play with ls -l /proc/self/fd/0 in case you need to assure yourself that this indeed is so).
A file describing a job has been deleted by the time a job is run. However, the file is still available for the kernel because it has been duplicated with dup(2) before being used as the standard input for a job. So, actually we are resolving a symbolic link to a file name which is not visible any more. In the perl script at the end we need to take this into account as readlink will return something like /foo/bar/baz (deleted) instead of /foo/bar/baz. And we're interested in just the file name which has all the information we need.
The reason why the symbolic link points to a deleted file is because at daemon unlinks the original before executing the job. Unlinking gets done only after creating a copy, a hard link, which begins with = instead of a. With this the at daemon tries to ensure there will be only one copy of a job running: the daemon will not execle(2), ie. it will bail out, should the link(2) fail. Because the original file has been subject to open(2) and dup(2) the inode is still there for the kernel to use because it still has hard links pointing to it.
After a fairly long and possibly confusing introduction, here is how to put it all together:
#!/usr/bin/perl
use strict;
use warnings;
my $job_file = readlink("/proc/self/fd/0");
if (index($job_file, " ") > 0) {
$job_file = substr($job_file, 0, index($job_file, " ") - 1);
}
my $tmp = substr($job_file, rindex($job_file, "/") + 1);
$tmp =~ s/^a([0-9a-f]{5})[0-9a-f]+/$1/;
my $job_id = hex($tmp);
if ($job_id > 0) {
printf("My AT job id is %d.\n", $job_id);
}
# end of file.
Related
I have defined a variable inside one of the shell script to create the file name with date value in it.
I used "date +%Y%m%d" command to insert the current date which was defined in date_val variable.
And I have defined the filename variable to have "${path}/sample_${date_val}.txt
For few days it was creating the file name properly as /programfiles/sample_20180308.txt
But today the filename was created without date as /programfiles/sample_.txt
When I try to execute the command "date +%Y%m%d" in linux, it is returning the correct value - 20180309.
Any idea why the filename was created without the date value ??? . I did not modify anything in my script too. So wondering what might have gone wrong.
Sample excerpt of my script is given below for easy understanding :
EDITED
path=/programfiles
date_val=$(date +%Y%m%d )
file_name=${path}/sample_${date_val}.txt
Although incredibly unlikely, it's certainly possible for date to fail, based on the source code. Under the covers, it calls either clock_gettime() or gettimeofday(), both of which can fail.
The date program will also refuse to output anything to standard output if the date from either of those two functions is out of range during the call to (which is possible if they fail).
It's also possible that the date program could "disappear" for various reasons, such as actually being hidden or permissions changed, or a shortage of resources like file handles when attempting to open the executable.
As mentioned, all these possibilities are a stretch, unlikely to happen in the real world.
If you want to handle the case where you get inadequate output from date, you can simply try until you get a valid one, something like (with the possibility of adding some limit to detect if it's never any good):
todaysDate="$(date +%Y%m%d)"
while [[ ! $x =~ ^[0-9]{8}$ ]] ; do
sleep 1
todaysDate="$(date +%Y%m%d)"
done
# todaysDate now guaranteed to be eight digits.
I'd like to send myself a text when a job is finished. I understand how to change the job name so that the .o and .e files have the appropriate name. But I'm not sure if there's a way to change the job ID from a string of numbers to a specified key so I know which job it is. I usually have a lot of different jobs going at once, so it's difficult to remember all the different job ID numbers. Is there a way in the .pbs script to change the job ID so that when I get the message I can see which job it is rather than just a string of numbers?
If you are using Torque and add the -N flag, then you can add a name to the job. It will still use the numeric portion of the job id as part of the output and error filenames, but this allows you to add something to help you distinguish among your jobs. For example:
$ echo ls | qsub -N whatevernameyouplease
I have basic knowledge of linux bash shell scripting, right now I am facing a problem that is like following:
Suppose I am working in an empty directory mydir
Then there is a process which is created by a C program to generate a file with one word. (Exp: file.txt would have one word, "hello")
Routinely, after a specific period of time, the file is updated by the C program with the same one word "hello".
I want check the file every time when it is updated.
But the issue is that I also want my script doing some other operation while checking the file updates and when it detects file updates that it returns something for which I can use to trigger something else.
So, can anyone help me.
Also, some proof of concept :
while true;
do
func1();
func2();
check file is updated or not
if updated ; then
break;
else
continue;
You probably want the stat command. Do man stat to see how yours works. You want to look for "modtime" or "time of last data modification" option. For mine that would be stat -c%Y file. Something like basemodtime=$(stat -c%Y file) before the loop, modtime=$(stat -c%Y file) after func2(), and then if [ $modtime != $basemodtime ]; then to detect "updated".
I have a cron task that runs periodically. This task depends on a condition to be valid in order to complete its processing. In case it matters this condition is just a SELECT for specific records in the database. If the condition is not satisfied (i.e the SELECT does not return the result set expected) then the script exits immediately.
This is bad as the condition would be valid soon enough (don't know how soon but it will be valid due to the run of another script).
So I would like somehow to make the script more robust. I thought of 2 solutions:
Put a while loop and sleep constantly until the condition is
valid. This should work but it has the downside that once the script
is in the loop, it is out of control. So I though to additionally
after waking up to check is a specific file exists. If it does it
"understands" that the user wants to "force" stop it.
Once the script figures out that the condition is not valid yet it
appends a script in crontab and stops. That seconds script
continually polls for the condition and if the condition is valid
then restart the first script to restart its processing. This solution to me it seems to work but I am not sure if it is a good solution. E.g. perhaps programatically modifying the crontab is a bad idea?
Anyway, I thought that perhaps this problem is common and could have a standard solution, much better than the 2 I came up with. Does anyone have a better proposal? Which from my ideas would be best? I am not very experienced with cron tasks so there could be things/problems I could be overseeing.
instead of programmatically appending the crontab, you might want to consider using at to schedule the job to run again at some time in the future. If the script determines that it cannot do its job now, it can simply schedule itself to run again a few minutes (or a few hours, as it may) later by way of an at command.
Following up from our conversation in comments, you can take advantage of conditional execution in a cron entry. Supposing you want to branch based on time of day, you might use the output from date.
For example: this would always invoke the first command, then invoke the second command only if the clock hour is currently 11:
echo 'ScriptA running' ; [ $(date +%H) == 11 ] && echo 'ScriptB running'
More examples!
To check the return value from the first command:
echo 'ScriptA' ; [ $? == 0 ] echo 'ScriptB'
To instead check the STDOUT, you can use as colon as a noop and branch by capturing output with the same $() construct we used with date:
: ; [ $(echo 'ScriptA') == 'ScriptA' ] && echo 'ScriptB'
One downside on the last example: STDOUT from the first command won't be printed to the console. You could capture it to a variable which you echo out, or write it to a file with tee, if that's important.
I have a perl script the creates a report based on an xml definition. Currently these definitions all exist as .xml files.
So I have the script run-report.pl, which can take a path to a definition file and create the report.
Now I want to create run-reports-from-db.pl, which will generate the report definition based on same database entries. I don't want to create temp files to pass to run-report.pl, I would just like to pass in the definition somehow.
So instead of saying:
run-report.pl -def=./path/to/def.xml
I want to be able to say:
run-report.pl --stream
And have the report definition available in <STDIN>
I am sure there is pretty trivial way to do this???
If I understand your question correctly, all you need is one | (pipe).
./generate-xml-from-db.pl | ./run-report.pl --stream
Anything the first process in the pipeline prints to stdout will appear in the second process's stdin.
As long as you read from STDIN, you have it available. Notice what happens with you take the code below name it something like echo.pl run it at the command line and paste reams of text.
#!/usr/bin/perl -w
use 5.010;
use strict;
use warnings;
while ( <> ) {
say;
}
<> is the Perl shorthand for "read from STDIN".
As long as the method you're using to launch the process has a way to get a hold of the standard input and outputs, you can just write it to that handle. You have to use the ways that are available to you. In Java, for example, you'd have to get the input stream of the process, in a batch command you have to pipe it. At a GUI terminal you can cut and paste.