How to view and read cron logs on Ubuntu, Debian and CentOS?
Cron can generate logs, which are very useful in troubleshooting your cron jobs. In this quick tutorial, we will take a look at cron logs – how to find them and how to read them.
Where are cron logs stored?
By default, all cron logs are stored in the main system log which is located in /var/log/syslog on Ubuntu and Debian systems and in /var/log/cron on CentOS.
You can filter cron logs in the system log by running the grep command.
This applies to Ubuntu and Debian. On CentOS, simply replace the system log directory to /var/log/cron and you are good to go.
How to set up cron.log file?
Another way you can monitor cron logs is to set up separate log file especially for cron logs.
To do this, open the /etc/rsyslog.d/50-default.conf configuration file in the nano editor using the following command:
This will open the configuration file for editing. In this file, uncomment the highlighted line to enable logging cron logs into the /var/log/cron.log file.
The highlighted line should look like this:
We are not done yet. Now we need to create the /var/log/cron.log file. To do this, simply run the following command:
Save the empty file and exit. Then restart the rsyslog service:
At this point, all cron logs are stored in the /var/log/cron.log file.
How to watch cron logs in real-time?
To view cron logs in real-time, create watchcron file using the following command:
Add the following line in the file. Then save and exit the file.
This will refresh the logs event page after 10 seconds and displays the last 15 events on the page.
Add the executable permission to the newly created watchcron file:
And finally, copy this file in /usr/sbin location using the following command:
Now to watch cron log in real-time, simply type watchcron in the terminal and hit enter.
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Cron is a command-line job scheduler on Unix-like systems. It allows you to run automated tasks in the background and it's especially useful for repetitive jobs.
One of the neat features of Cron is the ability to send emails when an error occurs during the execution of the cronjob. This can be done using the `MAILTO` environmental variable. When executing cronjob, any output is mailed to the owner of the crontab or to the user or email address specified in the `MAILTO` environment variable in the crontab, if such exists.
Sometimes you may find that duplicate cronjobs are running at the same time. This may happen when the cronjob takes longer to complete than its execution interval. Here is a simple way to prevent this from happening ever again.
In this quick tutorial, we will take a look at how to set up a cron job to run at a specific time.
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Как проверить журналы cron в Linux?
Советы и хитрости
В среде Linux чаще всего используется слово «cron jobs». Для тех, кто не знает об этом. Задание cron — это планировщик задач, который автоматизирует все повторяющиеся задачи в дистрибутиве Linux. Задания Cron выполняются в указанную дату и время, которые планируются системным администратором. Таким образом, журналы или история заданий cron хранятся в файле журнала, который помогает системному администратору проверить, выполняются ли задания cron в указанное время или нет.
В этой статье мы обсудим, как пользователь может просматривать файлы журналов cron в среде Linux. Мы выполнили все задачи в системе Ubuntu 20.04, которые помогут вам лучше понять журналы cron.
Откройте терминал, нажав сочетание клавиш Ctrl + Alt + t. Теперь, используя следующие два разных метода, можно легко получить доступ к событиям журнала cron:
Метод 1: проверьте события журналов cron через системный журнал
Это очень простой и легкий способ проверить, выполняются ли в вашей системе события журнала cron. Войдите в систему как пользователь root на терминале и введите следующую команду:
Следующие события журналов cron должны отображаться на терминале:
Метод 2: мониторинг журналов cron путем настройки файла cron.log
Рекомендуемый способ — создать отдельный файл cron.log для отслеживания или проверки событий журналов cron в вашей системе Linux. Для этого откройте файл /etc/rsyslog.d/50-default.conf, выполнив следующую команду:
Найдите в этом файле ’# cron. * /Var/log/cron.log’ и раскомментируйте эту строку, которая также показана на следующем снимке экрана:
Теперь создайте cron.log с помощью любого исходного кода или текстового редактора.
Перезапустите службу rsyslog, а затем проверьте состояние работы этой службы в вашей системе с помощью следующей команды:
$ sudo systemctl restart rsyslog
$ sudo systemctl status rsyslog
В окне терминала должен быть напечатан следующий вывод:
Теперь все события журнала cron должны сохраняться в файле cron.log.
Для просмотра в реальном времени cron регистрирует события с помощью команды watchcron. Итак, создайте файл watchcron следующим образом:
Добавьте в этот файл следующие строки:
#!/bin/bash
watch -n 10 tail -n 25 / var / log / cron.log
Сохраните этот файл в nano, используя Ctrl + o, а затем нажмите Ctrl + x, чтобы выйти из этой среды.
Здесь указанный сторожевой кронштейн обновляет страницу журналов событий через 10 секунд и отображает последние 25 событий на странице.
Установите разрешения для исполняемого файла для этого файла с помощью следующей команды:
Скопируйте этот файл в папку ’/ usr / sbin’ следующим образом:
Теперь, чтобы проверить события журналов cron в реальном времени, выполните на терминале следующую команду:
На терминале появится следующее окно:
Заключение
В этой статье мы объяснили, как вы можете проверять или отслеживать события журналов cron в режиме реального времени с помощью одной команды watchcron.
Where is the cron / crontab log?
I want to verify that my cron job is executing and at what time. I believe there is a log for my sudo crontab -e jobs, but where?
I searched google and found recommendations to look in /var/log (in which I do not see anything with ‘cron’ in the name) and to edit the file /etc/syslog.conf which I also do not have.
15 Answers 15
On a default installation the cron jobs get logged to
You can see just cron jobs in that logfile by running
If you haven’t reconfigured anything,the entries will be in there.
You can create a cron.log file to contain just the CRON entries that show up in syslog. Note that CRON jobs will still show up in syslog if you follow the following directions.
Find the line that starts with:
uncomment that line, save the file, and restart rsyslog:
You should now see a cron log file here:
Cron activity will now be logged to this file (in addition to syslog).
Note that in cron.log you will see entries for when cron ran scripts in /etc/cron.hourly, cron.daily, etc. — e.g. something like:
However, you will not see more information about what scripts were actually ran inside /etc/cron.daily or /etc/cron.hourly, unless those scripts direct output to the cron.log (or perhaps to some other log file).
If you want to verify if a crontab is running and not have to search for it in cron.log or syslog, create a crontab that redirects output to a log file of your choice — something like:
This will redirect all standard output and errors that may be produced by the script that is run to the log file specified.
How to log cron jobs?
I want to know how I can see exactly what the cron jobs are doing on each execution. Where are the log files located? Or can I send the output to my email? I have set the email address to send the log when the cron job runs but I haven’t received anything yet.
9 Answers 9
will log all output from the cron job to /var/log/myjob.log
You might use mail to send emails. Most systems will send unhandled cron job output by email to root or the corresponding user.
By default cron logs to /var/log/syslog so you can see cron related entries by using:
There are at least three different types of logging:
The logging BEFORE the program is executed, which only logs IF the cronjob TRIED to execute the command. That one is located in /var/log/syslog, as already mentioned by @Matthew Lock.
The logging of errors AFTER the program tried to execute, which can be sent to an email or to a file, as mentioned by @Spliffster. I prefer logging to a file, because with email THEN you have a NEW source of problems, and its checking if email sending and reception is working perfectly. Sometimes it is, sometimes it’s not. For example, in a simple common desktop machine in which you are not interested in configuring an smtp, sometimes you will prefer logging to a file:
- I would also consider checking the permissions of /ABSOLUTE_PATH_TO_LOG, and run the command from that user’s permissions. Just for verification, while you test whether it might be a potential source of problems.
There are some common sources of problems with cronjobs: * The ABSOLUTE PATH of the binary to be executed. When you run it from your shell, it might work, but the cron process seems to use another environment, and hence it doesn’t always find binaries if you don’t use the absolute path. * The LIBRARIES used by a binary. It’s more or less the same previous point, but make sure that, if simply putting the NAME of the command, is referring to exactly the binary which uses the very same library, or better, check if the binary you are referring with the absolute path is the very same you refer when you use the console directly. The binaries can be found using the locate command, for example:
Be sure that the binary you will refer, is the very same the binary you are calling in your shell, or simply test again in your shell using the absolute path that you plan to put in the cronjob.
- Another common source of problems is the syntax in the cronjob. Remember that there are special characters you can use for lists (commas), to define ranges (dashes -), to define increment of ranges (slashes), etc. Take a look: http://www.softpanorama.org/Utilities/cron.shtml
Here is my code:
On Ubuntu you can enable a cron.log file to contain just the CRON entries.
Uncomment the line that mentions cron in /etc/rsyslog.d/50-default.conf file:
Save and close the file and then restart the rsyslog service:
You can now see cron log entries in its own file:
However, you will not see more information about what scripts were actually run inside /etc/cron.daily or /etc/cron.hourly , unless those scripts direct output to the cron.log (or perhaps to some other log file).
If you want to verify if a crontab is running and not have to search for it in cron.log or syslog , create a crontab that redirects output to a log file of your choice — something like:
cron already sends the standard output and standard error of every job it runs by mail to the owner of the cron job.
You can use MAILTO=recipient in the crontab file to have the emails sent to a different account.
For this to work, you need to have mail working properly. Delivering to a local mailbox is usually not a problem (in fact, chances are ls -l «$MAIL» will reveal that you have already been receiving some) but getting it off the box and out onto the internet requires the MTA (Postfix, Sendmail, what have you) to be properly configured to connect to the world.
If there is no output, no email will be generated.
A common arrangement is to redirect output to a file, in which case of course the cron daemon won’t see the job return any output. A variant is to redirect standard output to a file (or write the script so it never prints anything — perhaps it stores results in a database instead, or performs maintenance tasks which simply don’t output anything?) and only receive an email if there is an error message.
To redirect both output streams, the syntax is
Notice how we append (double >> ) instead of overwrite, so that any previous job’s output is not replaced by the next one’s.
As suggested in many answers here, you can have both output streams be sent to a single file; replace the second redirection with 2>&1 to say «standard error should go wherever standard output is going». (But I don’t particularly endorse this practice. It mainly makes sense if you don’t really expect anything on standard output, but may have overlooked something, perhaps coming from an external tool which is called from your script.)
cron jobs run in your home directory, so any relative file names should be relative to that. If you want to write outside of your home directory, you obviously need to separately make sure you have write access to that destination file.
A common antipattern is to redirect everything to /dev/null (and then ask Stack Overflow to help you figure out what went wrong when something is not working; but we can’t see the lost output, either!)
From within your script, make sure to keep regular output (actual results, ideally in machine-readable form) and diagnostics (usually formatted for a human reader) separate. In a shell script,