I am running ubuntu 13.10 and want to write a bash script that will execute a given task at non-pre-determined time intervals. My understanding of this is that cronjobs require me to know when the task will be performed again. Thus, I was recommended to use "at."
I'm having a bit of trouble using "at." Based on some experimentation, I've found that
echo "hello" | at now + 1 minutes
will run in my terminal (with and without quotes). Running "atq" results in my computer telling me that the command is in the queue. However, I never see the results of the command. I assume that I'm doing something wrong, but the manpages don't seem to be telling me anything useful.
Thanks in advance for any help.
Besides the fact that commands are run without a terminal (output and input is probably redirected to /dev/null), your command would also not run since what you're passing to at is not echo hello but just hello. Unless hello is really an existing command, it won't run. What you want probably is:
echo "echo hello" | at now + 1 minutes
If you want to know if your command is really running, try redirecting the output to a file:
echo "echo hello > /var/tmp/hello.out" | at now + 1 minutes
Check the file later.
Related
I'm setting a cron job that is a bash script containing the below:
#!/bin/bash
NUM_CONTAINERS=$(docker ps -q | wc -l)
if [ $NUM_CONTAINERS -lt 40 ]
then
echo "Time: $(date). Restart containers."
cd /opt
pwd
sudo docker kill $(docker ps -q)
docker-compose up -d
echo "Completed."
else
echo Nothing to do
fi
The output is appended to a log file:
>> cron.log
However the output in the cron file only shows:
Time: Sun Aug 15 10:50:01 UTC 2021. Restart containers.
/opt
Completed.
Both command do not seem to execute as I don't see any change in my containers either.
These 2 non working commands work well in a standalone .sh script without condition though.
What am I doing wrong?
User running the cron has sudo privileges, and we can see the second echo printing.
Lots of times, things that work outside of cron don't work within cron because the environment is not set up in the same way.
You should generally capture standard output and error, to see if something going wrong.
For example, use >> cron.log 2>&1 in your crontab file, this will capture both.
There's at least the possibility that docker is not in your path or, even if it is, the docker commands are not working for some other reason (that you're not seeing since you only capture standard output).
Capturing standard error should help out with that, if it is indeed the issue.
As an aside, I tend to use full path names inside cron scripts, or set up very limited environments at the start to ensure everything works correctly (once I've established why it's not working correctly).
I am quite new to bash (barely any experience at all) and I need some help with a bash script.
I am using docker-compose to create multiple containers - for this example let's say 2 containers. The 2nd container will execute a bash command, but before that, I need to check that the 1st container is operational and fully configured. Instead of using a sleep command I want to create a bash script that will be located in the 2nd container and once executed do the following:
Execute a command and log the console output in a file
Read that file and check if a String is present. The command that I will execute in the previous step will take a few seconds (5 - 10) seconds to complete and I need to read the file after it has finished executing. I suppose i can add sleep to make sure the command is finished executing or is there a better way to do this?
If the string is not present I want to execute the same command again until I find the String I am looking for
Once I find the string I am looking for I want to exit the loop and execute a different command
I found out how to do this in Java, but if I need to do this in a bash script.
The docker-containers have alpine as an operating system, but I updated the Dockerfile to install bash.
I tried this solution, but it does not work.
#!/bin/bash
[command to be executed] > allout.txt 2>&1
until
tail -n 0 -F /path/to/file | \
while read LINE
do
if echo "$LINE" | grep -q $string
then
echo -e "$string found in the console output"
fi
done
do
echo "String is not present. Executing command again"
sleep 5
[command to be executed] > allout.txt 2>&1
done
echo -e "String is found"
In your docker-compose file make use of depends_on option.
depends_on will take care of startup and shutdown sequence of your multiple containers.
But it does not check whether a container is ready before moving to another container startup. To handle this scenario check this out.
As described in this link,
You can use tools such as wait-for-it, dockerize, or sh-compatible wait-for. These are small wrapper scripts which you can include in your application’s image to poll a given host and port until it’s accepting TCP connections.
OR
Alternatively, write your own wrapper script to perform a more application-specific health check.
In case you don't want to make use of above tools then check this out. Here they use a combination of HEALTHCHECK and service_healthy condition as shown here. For complete example check this.
Just:
while :; do
# 1. Execute a command and log the console output in a file
command > output.log
# TODO: handle errors, etc.
# 2. Read that file and check if a String is present.
if grep -q "searched_string" output.log; then
# Once I find the string I am looking for I want to exit the loop
break;
fi
# 3. If the string is not present I want to execute the same command again until I find the String I am looking for
# add ex. sleep 0.1 for the loop to delay a little bit, not to use 100% cpu
done
# ...and execute a different command
different_command
You can timeout a command with timeout.
Notes:
colon is a utility that returns a zero exit status, much like true, I prefer while : instead of while true, they mean the same.
The code presented should work in any posix shell.
Specifics:
I'm trying to build a bash script which needs to do a couple of things.
Firstly, it needs to run a third party script that I cannot manipulate. This script will build a project and then start a node server which outputs data to the terminal continually. This process needs to continue indefinitely so I can't have any exit codes.
Secondly, I need to wait for a specific line of output from the first script, namely 'Started your app.'.
Once that line has been output to the terminal, I need to launch a separate set of commands, either from another subscript or from an if or while block, which will change a few lines of code in the project that was built by the first script to resolve some dependencies for a later step.
So, how can I capture the output of the first subscript and use that to run another set of commands when a particular line is output to the terminal, all while allowing the first script to run in the terminal, and without using timers and without creating a huge file from the output of subscript1 as it will run indefinitely?
Pseudo-code:
#!/usr/bin/env bash
# This script needs to stay running & will output to the terminal (at some point)
# a string that we need to wait/watch for to launch subscript2
sh subscript1
# This can't run until subscript1 has output a particular string to the terminal
# This could be another script, or an if or while block
sh subscript2
I have been beating my head against my desk for hours trying to get this to work. Any help would be appreciated!
I think this is a bad idea — much better to have subscript1 changed to be automation-friendly — but in theory you can write:
sh subscript1 \
| {
while IFS= read -r line ; do
printf '%s\n' "$line"
if [[ "$line" = 'Started your app.' ]] ; then
sh subscript2 &
break
fi
done
cat
}
I am starting ftam server (ft820.rc on CentOS 5) using bash version bash 3.0 and I am having an issue with starting it from the script, namely in the script I do
ssh -nq root#$ip /etc/init.d/ft820.rc start
and the script won't continue after this line, although when I do on the machine defined by $ip
/etc/init.d/ft820.rc start
I will get the prompt back just after the service is started.
This is the code for start in ft820.rc
SPOOLPATH=/usr/spool/vertel
BINPATH=/usr/bin/osi/ft820
CONFIGFILE=${SPOOLPATH}/ffs.cfg
# Set DBUSERID to any value at all. Just need to make sure it is non-null for
# lockclr to work properly.
DBUSERID=
export DBUSERID
# if startup requested then ...
if [ "$1" = "start" ]
then
mask=`umask`
umask 0000
# startup the lock manager
${BINPATH}/lockmgr -u 16
# update attribute database
${BINPATH}/fua ${CONFIGFILE} > /dev/null
# clear concurrency locks
${BINPATH}/finit -cy ${CONFIGFILE} >/dev/null
# startup filestore
${BINPATH}/ffs ${CONFIGFILE}
if [ $? = 0 ]
then
echo Vertel FT-820 Filestore running.
else
echo Error detected while starting Vertel FT-820 Filestore.
fi
umask $mask
I repost here (on request of #Patryk) what I put in the comments on the question:
"is it the same when doing the ssh... in the commandline? ie, can you indeed connect without entering a password, using the pair of private_local_key and the corresponding public_key that you previously inserted in the destination root#$ip:~/.ssh/authorized_keys file ? – Olivier Dulac 20 hours ago "
"you say that, at the commandline (and NOT in the script) you can ssh root#.... and it works without asking for your pwd ? (ie, it can then be run from a script?) – Olivier Dulac 20 hours ago "
" try the ssh without the '-n' and even without -nq at all : ssh root#$ip /etc/init.d/ft820.rc start (you could even add ssh -v , which will show you local (1:) and remote (2:) events in a very verbose way, helping in knowing where it gets stuck exactly) – Olivier Dulac 19 hours ago "
"also : before the "ssh..." line in the script, make another line with, for example: ssh root#ip "set ; pwd ; id ; whoami" and see if that works and shows the correct information. This may help be sure the ssh part is working. The "set" part will also show you the running shell (ex: if it contains BASH= , you're running bash. Otherwise SHELL=... should give a good hint (sometimes not correct) about which shell gets invoked) – Olivier Dulac 19 hours ago "
" please try without the '-n' (= run in background and wait, instead of just run and then quit). It it doesn't work, try adding -t -t -t (3 times) to the ssh, to force it to allocate a tty. But first, please drop the '-n'. – Olivier Dulac 18 hours ago "
Apparently what worked was to add the -t option to the ssh command. (you can go up to put '-t -t -t' to further force it to try to allocate the tty, depending on the situation)
I guess it's because the invoked command expected to be run within an interactive session, and so needed a "tty" to be the stdout
A possibility (but just a wild guess) : the invoked rc script outputs information, but in a buffered environment (ie, when not launched via your terminal), the calling script couldn't see enough lines to fill the buffer and start printing anything out (like when you do a "grep something | somethings else" in a buffered environment and ctrl+c before the buffer was big enough to display anything : you end up thinking no lines were foudn by the grep, whereas there was maybe a few lines already in the buffer). There is tons to be said about buffering, and I am just beginning to read about it all. forcing ssh to allocate a tty made the called command think it was outputting to a live terminal session, and that may have turned off the buffering and allowed the result to show. Maybe in the first case, it worked too, but you could never see the output?
Not having much luck Googling this question and I thought about posting it on SF, but it actually seems like a development question. If not, please feel free to migrate.
So, I have a script that runs via cron every morning at about 3 am. I also run the same scripts manually sometimes. The problem is that every time I run my script manually and it fails, it sends me an e-mail; even though I can look at the output and view the error in the console.
Is there a way for the bash script to tell that it's being run through cron (perhaps by using whoami) and only send the e-mail if so? I'd love to stop receiving emails when I'm doing my testing...
you can try "tty" to see if it's run by a terminal or not. that won't tell you that it's specifically run by cron, but you can tell if its "not a user as a prompt".
you can also get your parent-pid and follow it up the tree to look for cron, though that's a little heavy-handed.
I had a similar issue. I solved it with checking if stdout was a TTY. This is a check to see if you script runs in interactive mode:
if [ -t 1 ] ; then
echo "interacive mode";
else
#send mail
fi
I got this from: How to detect if my shell script is running through a pipe?
The -t test return true if file descriptor is open and refers to a terminal. '1' is stdout.
Here's two different options for you:
Take the emailing out of your script/program and let cron handle it. If you set the MAILTO variable in your crontab, cron will send anything printed out to that email address. eg:
MAILTO=youremail#example.com
# run five minutes after midnight, every day
5 0 * * * $HOME/bin/daily.job
Set an environment variable in your crontab that is used to determine if running under cron. eg:
THIS_IS_CRON=1
# run five minutes after midnight, every day
5 0 * * * $HOME/bin/daily.job
and in your script something like
if [ -n "$THIS_IS_CRON" ]; then echo "I'm running in cron"; else echo "I'm not running in cron"; fi
Why not have a command line argument that is -t for testing or -c for cron.
Or better yet:
-e=email#address.com
If it's not specified, don't send an email.
I know the question is old, but I just came across the same problem. This was my solution:
CRON=$(pstree -s $$ | grep -q cron && echo true || echo false)
then test with
if $CRON
then
echo "Being run by cron"
else
echo "Not being run by cron"
fi
same idea as the one that #eruciform mentioned - follows your PID up the process tree checking for cron.
Note: This solution only works specifically for cron, unlike some of the other solutions, which work anytime the script is being run non-interactively.
What works for me is to check $TERM. Under cron it's "dumb" but under a shell it's something else. Use the set command in your terminal, then in a cron-script and check it out
if [ "dumb" == "$TERM" ]
then
echo "cron"
else
echo "term"
fi
I'd like to suggest a new answer to this highly-voted question. This works only on systemd systems with loginctl (e.g. Ubuntu 14.10+, RHEL/CentOS 7+) but is able to give a much more authoritative answer than previously presented solutions.
service=$(loginctl --property=Service show-session $(</proc/self/sessionid))
if [[ ${service#*=} == 'crond' ]]; then
echo "running in cron"
fi
To summarize: when used with systemd, crond (like sshd and others) creates a new session when it starts a job for a user. This session has an ID that is unique for the entire uptime of the machine. Each session has some properties, one of which is the name of the service that started it. loginctl can tell us the value of this property, which will be "crond" if and only if the session was actually started by crond.
Advantages over using environment variables:
No need to modify cron entries to add special invocations or environment variables
No possibility of an intermediate process modifying environment variables to create a false positive or false negative
Advantages over testing for tty:
No false positives in pipelines, startup scripts, etc
Advantages over checking the process tree:
No false positives from processes that also have crond in their name
No false negatives if the script is disowned
Many of the commands used in prior posts are not available on every system (pstree, loginctl, tty). This was the only thing that worked for me on a ten years old BusyBox/OpenWrt router that I'm currently using as a blacklist DNS server. It runs a script with an auto-update feature. Running from crontab, it sends an email out.
[ -z "$TERM" ] || [ "$TERM" = "dumb" ] && echo 'Crontab' || echo 'Interactive'
In an interactive shell the $TERM-variable returns the value vt102 for me. I included the check for "dumb" since #edoceo mentioned it worked for him. I didn't use '==' since it's not completely portable.
I also liked the idea from Tal, but also see the risk of having undefined returns. I ended up with a slightly modified version, which seems to work very smooth in my opinion:
CRON="$( pstree -s $$ | grep -c cron )"
So you can check for $CRON being 1 or 0 at any time.