I am really new to Linux and I apologize if this is rudimentary, but I have Google'd to find examples with no clarity and I am confused. (the question relates to a server running CentOs 6)
My questions are:
I am not sure what is the default directory that I should store a .sh file in so that a cron job can run it.
Is the syntax and sequence of my code in .sh file below correct?.
I have tested the TSQL and its fine.
#! SQL="DELETE FROM messages WHERE date < DATE_SUB(CURDATE(), INTERVAL 7 DAY)"
MYSQL_USER="root"
MYSQL_PASS="xxxxxx"
MYSQL_DB="mydb"
I understand that the cron should contain this to do it on a daily basis:
0 0 * * *
But I am just having some apprehension of how to put it all together so I don't screw things up. A full example or explanation or a reference link would be greatly appreciated.
I believe that cron will execute the script from whichever directory it is in, given that:
the file has execution permission for the user that cron runs as (usually root if job is configured in the system-wide crontab)
the cron line specifies the full path to the script
So, if your script is /opt/script.sh, specifying this in cron:
0 0 * * * /opt/script.sh
will execute script.sh each day in 12:00am.
Please note that if this is the system-wide crontab (/etc/crontab) it should also include a username as which to execute the command:
0 0 * * * username /opt/script.sh
Also, something to make sure when working with cron is to either use full paths when calling external commands from the script or to set up the PATH variable (either in the script itself or on the crontab file). This is needed because usually the environment in which cron jobs are run is pretty restricted.
Another thing to have in mind is that if any output is generated by a cron job this output is sent via mail to the user executing the cron. So to have some feedback from the script you have to either set up the system so that the mail message ends up in a mailbox which is read by a human being or the script sends all of it's output to a log file or syslog.
Related
When cron launches a command under my user ID, where in the file system does it actually launch it?
Let's say I have this python script:
import sys
filepath = sys.argv[1]
try:
fp= open(filepath)
... stuff ...
except:
print ("File not found.")
And I call the script in my crontab:
0 2 * * /home/me/scripts/bla.py filename
The file "filename" lives in /home/me/scripts. This gives me the 'File not found' message. So obviously my script got launched in some other place than /home/me/scripts. But where? I can put absolute paths into the crontab, but that's lots of clutter when multiple arguments are given. What's the best trick?
You don't say what system you're using, but on every system I've ever used cron launches jobs with their current working directory set to the user's home directory. Some systems will document that behaviour in their man pages for cron or crontab, but if they don't (or if you want to be certain) then it's easy to check the situation for your system. Just add this into your crontab:
* * * * * /bin/pwd > $HOME/cron-pwd.txt
and wait for a minute or so for the cron-pwd.txt file to appear in your home directory. And, obviously, remove that line from your crontab after you've read the file.
This means that your crontab command line can use pathnames relative to your home directory:
0 2 * * * scripts/bla.py scripts/filename
or you can build absolute paths by using the $HOME environment variable:
0 2 * * * $HOME/scripts/bla.py $HOME/scripts/filename
Alternatively, if writing out paths repeatedly isn't convenient then you can have your job change its own working directory before it starts running the program that will do the real work:
0 2 * * * cd $HOME/scripts ; ./bla.py filename
Some implementations of cron have enhancements that can affect the initial working directory, such as letting you specify a HOME environment variable that is different from your actual home directory. I don't recommend using that feature to get your job launched in a specific directory unless you're very sure of what you're doing, because setting a non-standard $HOME can have unexpected side effects on commands that get executed as part of the job.
BTW, your question has only 0 2 * * at the start of the crontab line, missing a field. I assume that's just a copy-paste error. Also, it doesn't invoke Python to run the script. I assume that's also either a copy-paste error or your real script has a #! line that invokes your Python interpreter.
I want to use cron for execute a script periodically. I want to try a simple script first but it does not work.
This is my script (scritp.sh) which permission are 700:
#!/bin/sh
clear
echo "Hello!"
mkdir Hello
And this is the crontab file when I edit it with the command crontab -e:
SHELL=/bin/sh
* * * * * /home/padro/Documents/script.sh
EDIT:
I have that script on /home/padro/Documents folder. What I do after it is execute the command crontab -e for modify the cron file. In this file I put the shell that I want SHELL=/bin/sh and also the cron schedule expression * * * * * /home/padro/Documents/script.sh. This schedule teorically run the script every minute. Finally I save the file and when a minute passes I can't see the echo of the script on the terminal.
EDIT2:
I have added mkdir hello, because I don't know if the echo of the script is shown on the terminal. But the hello directory is never created.
Any output generated by a program called from cron will by default be emailed to the user owning the crontab (assuming local delivery of mail messages is possible). So I'd suggest that you look in your inbox on the local machine.
To save the output into a file, use a redirection in the crontab, or arrange for the script to write its output to a file.
Jobs started by cron does not run with a terminal, so you should not expect to see your terminal being cleared every minute by running this script through cron.
The Hello folder should have been created in the working directory used by the script (possibly your home directory). To make absolutely sure you know where the script's working directory is, use cd in the script to move to the correct location.
I do not have enough reputation to add comment.
My humble comment would be.
Is the cron file you mentioned via root?
cos chmod 700 a file would be only be executed by owner.
If you are using redhat linux, the user account you use on the first log in is user rights NOT root.
Reference link to a cheat sheet.
su - root
system will prompt root password
crontab -e
* * * * * /home/padro/Documents/script.sh
You can even run a test script, which I did encounter the similar situation as you when I first learnt scripting into your crontab-
* * * * * date > export/home/padro/Documents/testing.txt
If you could, restart the server.
Check if your directory is correct using the command
pwd in linux/unix.
I hope my comment based on my recent learning have helped you.
Edit 1: Remove clear in your script. Thanks...
Edit 2: I believe your Hello folder is created at the core of the root folder try looking for it... or the home directory of the user...
I have my php script file in /var/www/html/dbsync/index.php. When cd /var/www/html/dbsync/ and run php index.php it works perfectly.
I want to call PHP file through sh file, the location of SH file is as below
/var/www/html/dbsync/dbsync.sh
This is the content of the dbsync.sh file is:
/usr/bin/php /var/www/html/dbsync/index.php >> /var/www/html/dbsync/myscript.log 2>&1 -q -f
When I cd /var/www/html/dbsync/ and run ./dbsync.sh it works perfectly as well.
Now if I set up crontab as below:
1 * * * * /var/www/html/dbsync/dbsync.sh /var/www/html/dbsync
However, this crontab is not working as expected.
What can be wrong?
As seen in comments, the problem is that you are not defining what program should be used to execute the script. Take into account that a cronjob is executed in a tiny environment; there, not much can be assumed. This is why we define full paths, etc.
So you need to say something like:
1 * * * * /bin/sh /var/www/html/dbsync/dbsync.sh /var/www/html/dbsync
# ^^^^^^^
/bin/sh being the binary you want to use to execute the script.
Otherwise, you can set execution permissions to the script and add a shell-script header telling it what interpreter to use:
#!/bin/sh
If you do this, adding the path of the binary is not necessary.
From Troubleshooting common issues with cron jobs:
Using relative paths. If your cron job is executing a script of some
kind, you must be sure to use only absolute paths inside that script.
For example, if your script is located at /path/to/script.phpand
you're trying to open a file called file.php in the same directory,
you cannot use a relative path such as fopen(file.php). The file must
be called from its absolute path, like this: fopen(/path/to/file.php).
This is because cron jobs do not necessarily run from the directory in
which the script is located, so all paths must be called specifically.
Also, I understand you want to run this every minute. If so, 1 * * * * won't do. Intead, it will run at every 1st minute past every hour. So if you want to run it every minute, say * * * * *.
It is important to understand "login shell" and "interactive shell" what they means.
login shell: is briefly when you sign in with ssh session and get a terminal window where you can enter shell commands. After login the system executes some files(.bashrc) and sets some environment variables such as the PATH variable for you.
interactive shell :After login on a system, you can startup manually shell terminal(s). The system executes some profile file assigned to your account (.bash_profile, .bash_login,.profile). This files also sets some environment variables and initialize PATH variable for your manually opened shell session.
By OS started shell scripts and cron jobs does not fit in above mentioned way for starting a shell. Therefore no any system scripts(.bashrc) or user profiles are executed. This means our PATH variable is not initialized. Shell commands could not found because PATH variable does not point to right places.
This explains why your script runs successfully if you start it manually but fails when you start it via crontab.
Solution-1:
Use absolute path of every shell command instead of only the command name used in your script file(s).
instead of "awk" use "/usr/bin/awk"
instead of "sed" use "/bin/sed"
Solution-2: Initialize environment variables and especially the PATH variable before executing shell scripts!
method 1, add this header in your dbsync.sh:
#!/bin/bash -l
method 2, add bash -l in your cron file:
1 * * * * bash -l /var/www/html/dbsync/dbsync.sh /var/www/html/dbsync
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Possible Duplicate:
Cron job on Ubuntu for php
I am running and ubuntu server and wanted to run a php script every day. I have done some research and found that cron is the best way of doing this however, this is where i got stuck, a lot of the information on the internet about cron is very hard to follow and understand.
So i wanted to execute a simple php script once a day, the script i made for testing simply just deletes a record from a database, but the real script will do a lot more.
I tried setting up a task through plesk which is provided through my web host service but it didn't seem to execute when i wanted it to, i used 1 for minutes, 22 for hours, * for day, * for week and * for month and thought this would execute every day at 22:01.
I have the directories on my server:
cron.hourly
cron.daily
cron.weekly
cron.monthly
I thought i could dump i file in there and it would execute for example every day, but i'm guessing i need to make a cron script to call a php script right?
If i were to go the way of putting a file in the cron.daily folder how would i go about it?
Also if there are any steps i need to take on the php side please let me know?
Thanks a lot for your time.
There's couple of ways to setup cron job. Assuming you got shell access you could do crontab -e from console and define job there, i.e. like this:
1 22 * * * command
which would trigger command (whatever it is) at 22:01 each day (not sure why you set minutes to 1 instead of 0 though). To launch PHP script from there you would either have to install php-cli, and then invoke it that way:
1 22 * * * <path>/php -q script.php
You can also call bash script here, to setup all the stuff like paths etc and then call your php script form bash - sometimes it is simpler to do that way instead of crafting way too long command line for cron. And it's simpler to update it later. also, you could turn your php script into bash-runnable script by setting it execution bit (chmod a+x script.php) and adding shell's shebang:
#!/usr/bin/php -q
<?php
...
If your script got too many dependencies and you'd prefer to call it via web, you could use wget to mimic a browser. so your command would be:
/usr/bin/wget --delete-after --quiet --spider <URL-TO-YOUR-SCRIPT>
wget manual can be accessed by man wget or wget -h, or is on this website. Aternatively you may use HEAD tool from perl-www package - but it requires perl while wget is a standalone tool. If you use HTTPS with self signed certs, add --no-check-certificate to your invocation arguments. And you may also want to setup .htaccess and limit web access to your cron script to localhost/127.0.0.1
every minute:
* * * * * /path/script.php
every 24hours (every midnight):
0 0 * * * /path/script.php
Se this reference for how crontab works: http://adminschoice.com/crontab-quick-reference, and this handy tool to build cron jobx: http://www.htmlbasix.com/crontab.shtml
I'm using Ubuntu Linux 10.0.4. I want to run a script every 6 hours, every day. When I issue sudo crontab -e, I see:
# m h dom mon dow command
* 00,06,12,18 * * * /opt/scripts/selenium/run_nis_inf_tests.sh
However, I'm not seeing the expected outcome from my script, and I'm not even sure if its running. Is there a way to test, short of waiting until the specified time, that the script is running properly. Or, how can I view the errors the script is generating? - Dave
You can update the MAILTO variable to your email address, and cron should email you any STDOUT and STDERR output. Also check your syslog file /var/log/messages to see if the script is being executed by cron.
-Tony
Cron should mail it results so it looks like you have a problem.
Here, it seems you are missing a user to run the script as :
00,06,12,18 * * * user_name /opt/scripts/selenium/run_nis_inf_tests.sh
replace user_name by the name of the user the script needs to be run by, verify permissions of "run_nis_inf_tests.sh" and you should be ok.