Проверка crontab на ошибки

The syntax for the crontab entry looks correct. Indeed, if you edit your crontab using «crontab -e» (as you should), you’ll get an error if you specify a syntactically invalid crontab entry anyway.

1. Firstly, does /path_to_my_php_script/info.php run correctly from the command-line?

2. If so, does it also run correctly like this?:

   /bin/sh -c "(export PATH=/usr/bin:/bin; /path_to_my_php_script/info.php </dev/null)"
   

3. If that works, does it work like this?

   /bin/sh -c "(export PATH=/usr/bin:/bin; /path_to_my_php_script/info.php </dev/null >/dev/null 2>&1)"
   

Step (3) is similar to how cron will run your program (as documented in «man 5 cron».

The most likely problem you’re having is that the PATH cron is using to run your program is too restrictive. Therefore, you may wish to add something like the following to the top of your crontab entry (you’ll need to add in whatever directories your script will need):

PATH=~/bin:/usr/bin/:/bin

Also note that cron will by default use /bin/sh, not bash. If you need bash, also add this to the start of your crontab file:

SHELL=/bin/bash

Note that both those changes will affect all the crontab entries. If you just want to modify these values for your info.php program, you could do something like this:

*/2 * * * * /bin/bash -c ". ~/.bashrc; /path_to_my_php_script/info.php"

It’s also worth mentioning that on a system configured for «mail» (in other words a system which has an MTA configured [sendmail/postfix/etc]), all output from crontab programs is sent to you via email automatically. A default Ubuntu desktop system won’t have local mail configured, but if you’re working on a server you can just type «mail» in a terminal to see all those cron mails. This also applies to the «at» command.

Cron — это демон, который запускает задачи по указанному (заданному) времени и  который работает в наиболее распространенных дистрибутивах Unix / Linux. Поскольку cronjobs основаны на времени, иногда необходимо проверить и убедиться, что задание выполнялось в запланированное время. Иногда люди настраивают cron чтобы они отправляли вывод скрипта через системную почту или перенаправляюте вывод в файл; однако не все кроны настроены одинаково, и мние из них, могут быть настроены на отправку вывода в /dev/null, и тем самым, препятствуя любой возможности проверить выполняемое задание.

Создать cron задание

Первое что стоит проверить — это наличие ПИДа по крону:

# pgrep crond

Или:

# ps ax | grep crond | grep -Ev grep

crond, если он не настроен иначе, будет отправлять сообщение журнала в syslog каждый раз, когда он вызывает запланированное задание. Самый простой способ проверить работу cron на попытку срабатываания задание, — это проверить лог-файл.

В зависимости от Unix/Linux ОС, данный файл может иметь другое название.

Если у вас, CentOS/Fedora/RedHat, то просмотреть нужно:

# less /var/log/cron

Можно отсеять ненужное и поискать только необходимую крон-джобу, например:

# cat /var/log/cron| grep -E "back"

Nov 28 00:00:01 linux-notes CROND[212211]: (root) CMD (/usr/bin/bash /home/linux/scripts/backUPs.sh)
Dec 1 00:00:01 linux-notes CROND[126039]: (root) CMD (/usr/bin/bash /home/linux/scripts/backUPs.sh)

Собственно, все наглядно видно.

Если у вас, Ubuntu/Debian, то просмотреть нужно:

# less /var/log/syslog

Иногда, системные администраторы меняют вывод крона и для того, чтобы проверить куда пишуться логи по cron-job-ам, выполните:

# grep cron /etc/rsyslog.conf

*.info;mail.none;authpriv.none;cron.none                /var/log/messages
# Log cron stuff
cron.*                                                  /var/log/cron

С вывода видно, что у меня используется стандартный файл.

Так же, стоит проверить как настраивали крон-джобы:

# crontab -l

ИЛИ:

# crontab -l -u some_another_user

Возможно было перенаправление вывода в какой-то файл для дальнейшего анализа.

Стоит отметить, то — что некоторые кроны лежат тут:

# ls -lah /etc/cron.daily/
# ls -lah /etc/cron.hourly/
# ls -lah /etc/cron.weekly/
# ls -lah /etc/cron.monthly/

Бывает некоторые задачи запихивают туда.

Чтобы запретить или разрешить добавление крон-задат, нужно прописать юзера в:

# vim /etc/cron.d/cron.allow
# vim /etc/cron.d/cron.deny

Так же, можно восспользоватся следующими командами для проверки статуса, запуска/остановки/перезапуска службы:

# service cron status 
# service cron start 
# service cron stop
# service cron restart

Это все действия были для Linux, но сейчас приведу пример и для mac os x.

Недавно мне пришлось отлаживать работу Cron и проверять, действительно ли она выполняется по заданному расписанию. Я начал искать и проверять все логи и… нашел вроде бы подходящий файл для этого:

# grep cron /var/log/system.log

Но в нем не было признаков логирования крона!

Включить logging для Cron в Mac OSX

Открываем:

# vim /etc/syslog.conf

И прописываем:

cron.* /var/log/cron.log

Для перезапуска syslog-а, выполняем:

# launchctl unload /System/Library/LaunchDaemons/com.apple.syslogd.plist
# launchctl load /System/Library/LaunchDaemons/com.apple.syslogd.plist

Проверяем что получилось!

А для помощи, можно вызвать:

# man crontab

А на этом, у меня все, статья «Проверка работы cron в Unix/Linux» завершена.

The only reliable way I found is to check the log.

cron checks /etc/crontab every minute, and logs a message indicating that it has reloaded it, or that it found an error.

So after editing, run this:

sleep 60; grep crontab /var/log/syslog | tail

Or, to not wait a full minute, but only until the next minute + 5 seconds:

sleep $(( 60 - $(date +%S) + 5 )) && grep cron /var/log/syslog | tail

Example output with an error:

Jan  9 19:10:57 r530a cron[107258]: Error: bad minute; while reading /etc/crontab
Jan  9 19:10:57 r530a cron[107258]: (*system*) ERROR (Syntax error, this crontab file will be ignored)

Good output:

Jan  9 19:19:01 r530a cron[107258]: (*system*) RELOAD (/etc/crontab)

That’s on Debian 8. On other systems, cron might log to a different file.

(I thought I could avoid hunting for the right log file by using systemd’s journalctl -u cron, but that didn’t show me these log entries, and actually seems to have stopped logging cron events 2 days ago for some reason)

The cron job scheduler has been bundled with unix and linux operating systems for decades. It’s widely used and usually very reliable.
This guide will walk you through locating cron jobs on your server, validating their schedules, and debugging common problems.

In this guide

1. The common reasons cron jobs fail
2. What to do if your cron job isn’t running when expected
3. What to do if your cron job fails unexpectedly
4. What to do if nothing else works

The common reasons cron jobs fail

Cron jobs can fail for an infinite variety of reasons but at Cronitor we have observed common failure patterns that
can provide a useful starting point for your debugging process. In the rest of this guide, we will dive into these
common failures with suggestions and solutions.

If you’re adding a new cron job and it is not working…

• Schedule errors are easy to make

  Cron job schedule expressions are quirky and difficult to write. If your job didn’t run when you expected it to,
  the easiest thing to rule out is a mistake with the cron expression.

• Cron has subtle environment differences

  A common experience is to have a job that works flawlessly when run at the command line but fails whenever
  it’s run by cron. When this happens, eliminate these common failures:

  1. The command has an unresovable relative path like ../scripts. (Try an absolute path)
  2. The job uses environment variables. (Cron does not load .bashrc and similar files)
  3. The command uses advanced bash features (cron uses /bin/sh by default)

  Tip:Our free software, CronitorCLI, includes a shell command to test run any job the way cron does.

• There is a problem with permissions

  Invalid permissions can cause your cron jobs to fail in at least 3 ways. This guide will cover them all.

If your cron job stopped working suddenly…

• System resources have been depleted

  The most stable cron job is no match for a disk that is full or an OS that can’t spawn new threads. Check all the usual graphs to rule this out.

• You’ve reached an inflection point

  Cron jobs are often used for batch processing and other data-intensive tasks that can reveal the constraints of your stack. Jobs often work fine until your data size grows to a point where
  queries start timing-out or file transfers are too slow.

• Infrastructure drift occurs

  When app configuration and code changes are deployed it can be easy to overlook the cron jobs on each server. This causes infrastructure drift where hosts are retired or credentials change that break the forgotten cron jobs.

• Jobs have begun to overlap themselves

  Cron is a very simple scheduler that starts a job at the scheduled time, even if the previous invocation is still running. A small slow-down can lead to a pile-up of overlapped jobs sucking up available resources.

• A bug has been introduced

  Sometimes a failure has nothing to do with cron. It can be difficult to thoroughly test cron jobs in a development environment and a bug might exist only in production.

What to do if your cron job doesn’t run when expected

You may find that you have scheduled a cron job that is just not running when expected. Follow these steps to locate your scheduled job and diagnose the problem.

1. Locate the scheduled job

   Tip:If you know where your job is scheduled, skip this step

   Cron jobs are run by a system daemon called crond that watches several locations for scheduled jobs. The first step to understanding why your job didn’t start when expected
   is to find where your job is scheduled.

   Search manually for cron jobs on your server

   • Check your user crontab with crontab -l

     dev01: ~ $ crontab -l
     # Edit this file to introduce tasks to be run by cron.
     # m h  dom mon dow   command
     5 4 * * *      /var/cronitor/bin/database-backup.sh

   • Jobs are commonly created by adding a crontab file in /etc/cron.d/
   • System-level cron jobs can also be added as a line in /etc/crontab
   • Sometimes for easy scheduling, jobs are added to /etc/cron.hourly/, /etc/cron.daily/, /etc/cron.weekly/
     or /etc/cron.monthly/
   • It’s possible that the job was created in the crontab of another user. Go through each user’s crontab using crontab -u username -l

   Or, scan for cron jobs automatically with CronitorCLI

   • Install CronitorCLI for free

   • Run cronitor list to scan your system for cron jobs:
     

     

   If you can’t find your job but believe it was previously scheduled double check that you are on the correct server.

2. Validate your job schedule

   Once you have found your job, verify that it’s scheduled correctly. Cron schedules are commonly used because they are expressive and powerful, but like regular expressions can sometimes be difficult to read.
   We suggest using Crontab Guru to validate your schedule.

   • Paste the schedule expression from your crontab into the text field on Crontab Guru
   • Verify that the plaintext translation of your schedule is correct, and that the next scheduled execution times match your expectations
   • Check that the effective server timezone matches your expectation. In addition to checking system time using date,
     check your crontab file for TZ or CRON_TZ timezone declarations that would override system settings.
     For example, CRON_TZ=America/New_York

3. Check your permissions

   Invalid permissions can cause your cron jobs to fail in at least 3 ways:

   1. Jobs added as files in a /etc/cron.*/ directory must be owned by root. Files owned by other users will be ignored and you may see a message similar to
      WRONG FILE OWNER in your syslog.
   2. The command must be executable by the user that cron is running your job as. For example if your ubuntu user crontab invokes a script like
      database-backup.sh, ubuntu must have permission to execute the script. The most direct way is to ensure that the ubuntu
      user owns the file and then ensure execute permissions are available using chmod +x database-backup.sh.
   3. The user account must be allowed to use cron. First, if a /etc/cron.allow file exists, the user must be listed. Separately,
      the user cannot be in a /etc/cron.deny list.

   Related to the permissions problem, ensure that if your command string contains a % that it is escaped with a backslash.

4. Check that your cron job is running by finding the attempted execution in syslog

   When cron attempts to run a command, it logs it in syslog.
   By grepping syslog for the name of the command you found in a crontab file you can validate that your job is scheduled correctly and cron is running.

   • Begin by grepping for the command in /var/log/syslog (You will probably need root or sudo access.)

     dev01: ~ $ grep database-backup.sh /var/log/syslog
     Aug  5 4:05:01 dev01 CRON[2128]: (ubuntu) CMD (/var/cronitor/bin/database-backup.sh)

   • If you can’t find your command in the syslog it could be that the log has been rotated or cleared since your job ran. If possible, rule that out by updating the job to run every minute by changing its schedule to * * * * *.
   • If your command doesn’t appear as an entry in syslog within 2 minutes the problem could be with the underlying cron daemon known as crond. Rule this out quickly by verifying that cron is running by looking up its process ID. If cron is not running no process ID will be returned.

     dev01: ~ $ pgrep cron
     323

   • If you’ve located your job in a crontab file but persistently cannot find it referenced in syslog, double check that crond has correctly loaded your crontab file. The easiest way to do this is to force
     a reparse of your crontab by running EDITOR=true crontab -e from your command prompt. If everything is up to date you will see a message like No modification made. Any other
     message indicates that your crontab file was not reloaded after a previous update but has now been updated. This will also ensure that your crontab file is free of syntax errors.

If you can see in syslog that your job was scheduled and attempted to run correctly but still did not produce the expected result you can assume there is a problem with the command you are trying to run.

What to do if your cron job fails unexpectedly

Your cron jobs, like every other part of your system, will eventually fail. This section will walk you through testing your job and spotting common failures.

1. Test run your command like cron does

   When cron runs your command the environment is different from your normal command prompt in subtle but important ways. The first step to troubleshooting is to simulate the cron environment and
   run your command in an interactive shell.

   Run any command like cron does with CronitorCLI

   • Install CronitorCLI for free

   • To force a scheduled cron job to run immediately, use cronitor select to scan your system and present a list of jobs to choose from.
   • To simulate running any command the way cron does, use cronitor shell:
     

     

   Or, manually test run a command like cron does

   • If you are parsing a file in /etc/cron.d/ or /etc/crontab each line is allowed to have an effective «run as» username
     after the schedule and before the command itself. If this applies to your job, or if your job is in another user’s crontab, begin by opening a bash prompt as that user sudo -u username bash
   • By default, cron will run your command using /bin/sh, not the bash or zsh prompt you are familiar with. Double check your crontab file for an optional
     SHELL=/bin/bash declaration. If using the default /bin/sh shell, certain features that work in bash like [[command]] syntax will cause syntax errors under cron.
   • Unlike your interactive shell, cron doesn’t load your bashrc or bash_profile so any environment variables defined there are unavailable in your cron jobs. This is true even if you have a SHELL=/bin/bash declaration. To simulate this, create a command prompt with a clean environment.

     dev01: ~ $ env -i /bin/sh
     $

   • By default, cron will run commands with your home directory as the current working directory. To ensure you are running the command like cron does, run cd ~ at your prompt.
   • Paste the command to run (everything after the schedule or declared username) into the command prompt. If crontab is unable to run your command, this should fail too and will hopefully contain a useful error message.
     Common errors include invalid permissions, command not found, and command line syntax errors.
   • If no useful error message is available, double check any application logs your job is expected to produce, and ensure that you are not redirecting log and error messages.
     In linux, command >> /path/to/file will redirect console log messages to the specified file and command >> /path/to/file 2>&1 will redirect both the console log and error messages.
     Determine if your command has a verbose output or debug log flag that can be added to see additional details at runtime.
   • Ideally, if your job is failing under cron it will fail here too and you will see a useful error message, giving you a chance to modify and debug as needed. Common errors include file not found, misconfigured permissions, and commandline syntax errors.

2. Check for overlapping jobs

   At Cronitor our data shows that runtime durations increase over time for a large percentage of cron jobs. As your dataset and user base grows it’s normal to find yourself in a situation
   where cron starts an instance of your job before the previous one has finished. Depending on the nature of your job this might not be a problem, but several undesired side effects are possible:

   • Unexpected server or database load could impact other users
   • Locking of shared resources could cause deadlocks and prevent your jobs from ever completing successfully
   • Creation of an unanticipated race condition that might result in records being processed multiple times, amplifying server load and possibly impacting customers

   To verify if any instances of a job are running on your server presently, grep your process list. In this example, 3 job invocations are running simultaneously:

   dev01: ~ $ ps aux | grep database-backup.sh
   ubuntu           1343   0.0  0.1  2585948  12004   ??  S    31Jul18   1:04.15 /var/cronitor/bin/database-backup.sh
   ubuntu           3659   0.0  0.1  2544664    952   ??  S     1Aug18   0:34.35 /var/cronitor/bin/database-backup.sh
   ubuntu           7309   0.0  0.1  2544664   8012   ??  S     2Aug18   0:18.01 /var/cronitor/bin/database-backup.sh

   To quickly recover from this, first kill the overlapping jobs and then watch closely when your command is next scheduled to run. It’s possible that a one time failure cascaded into several overlapping instances.
   If it becomes clear that the job often takes longer than the interval between job invocations you may need to take additional steps, e.g.:

   • Increase the duration between invocations of your job. For example if your job runs every minute now, consider running it every other minute.
   • Use a tool like flock to ensure that only a single instance of your command is running at any given time. Using flock is easy. After installing
     from apt-get or yum you only need to prefix the command in your crontab:

   dev01: ~ $ crontab -l
   # Edit this file to introduce tasks to be run by cron.
   # m h  dom mon dow   command
   * * * * *      flock -w 0 /var/cronitor/bin/database-backup.sh

   Read more about flock from the man page.

What to do if nothing else works

Here are a few things you can try if you’ve followed this guide and find that your job works flawlessly when run from the cron-like command prompt but fails to complete successful under crontab.

• First get the most basic cron job working with a command like date >> /tmp/cronlog. This command will simply echo the execution time to the log file each time it runs. Schedule this to run every minute and tail the logfile for results.

• If your basic command works, replace it with your command. As a sanity check, verify if it works.

• If your command works by invoking a runtime like python some-command.py perform a few checks to determine that the runtime version and environment is correct. Each language runtime has quirks
  that can cause unexpected behavior under crontab.

  • For python you might find that your web app is using a virtual environment you need to invoke in your crontab.
  • For node a common problem is falling back to a much older version bundled with the distribution.
  • When using php you might run into the issue that custom settings or extensions that work in your web app
    are not working under cron or commandline because a different php.ini is loaded.

  If you are using a runtime to invoke your command double check that it’s pointing to the expected version from within the cron environment.

• If nothing else works, restart the cron daemon and hope it helps, stranger things have happened. The way to do this varies from distro to distro so it’s best to ask google.

Cronitor automatically finds and monitors cron jobs.  Complete your setup in minutes.

Get Started Free

  */2 * * * * /path_to_my_php_script/info.php >/dev/null 2>&1

 (CRON) error (grandchild #2788 failed with exit status 2)

 */2 * * * * /usr/bin/php /path_to_my_php_script/info.php >/dev/null 2>&1

Ответы:

PATH=~/bin:/usr/bin/:/bin

SHELL=/bin/bash

*/2 * * * * /bin/bash -c ". ~/.bashrc; /path_to_my_php_script/info.php"

service crond status
service crond stop
service crond start

service cron status
service cron stop
service cron start

grep cron /var/log/syslog

tail -f /var/log/syslog | grep --line-buffered cron

Jul 9 09:39:01 vm cron[1129]: Error: bad day-of-month; while reading /etc/cron.d/new 

crontab -l

* * * * * <command> #Runs every minute