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How to create symlink for latest file only?


 
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Top Forums Shell Programming and Scripting How to create symlink for latest file only?
# 8  
Yes, and ensure a successful cd:
Code:
cd /var/log && ln -s "$(ls -r *error_log.* | head -1)" error_log

BTW ls -r is good here; ls -t would really sort by mtime.
# 9  
Quote:
Originally Posted by MadeInGermany
Yes, and ensure a successful cd:
Code:
cd /var/log && ln -s "$(ls -r *error_log.* | head -1)" error_log

BTW ls -r is good here; ls -t would really sort by mtime.
I gave below command in crontab, it executes, but failed with rc-2
Code:
13 16 * * * cd /var/log/apache && ln -s $(ls -r *error_log.* | head -1) error_log
14 16 * * * unlink /var/log/apache/error_log

From /var/cron/log -->

>  CMD: cd /var/log/apache && ln -s $(ls -r *error_log.* | head -1) error_log
>  root 16954 c Thu Apr 18 16:09:00 2019
<  root 16954 c Thu Apr 18 16:09:00 2019 rc=2


Last edited by solaris_1977; 04-18-2019 at 08:15 PM..
# 10  
That is not very surprising. You try to create a symlink at 4:13 pm (which fails because a symlink by that name already exists) and then you remove the symlink at 4:14 pm.

Furthermore, due to occasionally heavy load conditions, there is no guarantee that one cron job scheduled to start at a given time will complete before another job scheduled to run one minute later.

Why not do both in one step (assuming that you aren't really trying to create a symbolic link that has a one minute lifetime):
Code:
13 16 * * * cd /var/log/apache && rm -f error_log && ln -s $(ls -r *error_log.* | head -1) error_log


Last edited by Don Cragun; 04-19-2019 at 03:47 AM.. Reason: Fix typo: s/lifetime:/lifetime):/
These 2 Users Gave Thanks to Don Cragun For This Post:
# 11  
I'm a bit surprised that both the log entries are at 16:09h when the crontab entries are for 16:13h and 16:14h? Sure they belong together?
# 12  
May be I missed to copy correct content. Here I tried it again. I made two attemps. One job created for 23:58 and another time at 00:01
Code:
-bash-3.2# crontab -l | tail -2
58 23 * * * cd /var/log/apache && rm -f error_log && ln -s $(ls -r *error_log.* | head -1) error_log
01 00 * * * cd /var/log/apache && rm -f error_log && ln -s $(ls -r *error_log.* | head -1) error_log
-bash-3.2#
-bash-3.2# tail -f  /var/cron/log
<  root 28826 c Thu Apr 18 16:13:00 2019 rc=2
>  CMD: unlink /var/log/apache/error_log
>  root 29897 c Thu Apr 18 16:14:00 2019
<  root 29897 c Thu Apr 18 16:14:00 2019 rc=255
>  CMD:  cd /var/log/apache && rm -f error_log && ln -s $(ls -r *error_log.* | head -1) error_log
>  root 26545 c Thu Apr 18 23:58:00 2019
<  root 26545 c Thu Apr 18 23:58:00 2019 rc=2
>  CMD: cd /var/log/apache && rm -f error_log && ln -s $(ls -r *error_log.* | head -1) error_log
>  root 3093 c Fri Apr 19 00:01:00 2019
<  root 3093 c Fri Apr 19 00:01:00 2019 rc=2
^C
-bash-3.2# ls -l /var/log/apache/error_log
/var/log/apache/error_log: No such file or directory
-bash-3.2#

But if I run command manually, it is able to create
Code:
-bash-3.2# cd /var/log/apache && rm -f error_log && ln -s $(ls -r *error_log.* | head -1) error_log
-bash-3.2# ls -l /var/log/apache/error_log
lrwxrwxrwx   1 root     root          18 Apr 19 00:03 /var/log/apache/error_log -> error_log.20190419
-bash-3.2# rm -f error_log
-bash-3.2#

To test, if cron is working with root, I made another entry of date command
Code:
32 00 * * * date>/tmp/date.out

-bash-3.2# tail -f  /var/cron/log
<  root 20623 c Fri Apr 19 00:20:22 2019
>  CMD: date > /tmp/date.out
>  root 10651 c Fri Apr 19 00:26:00 2019
<  root 10651 c Fri Apr 19 00:26:00 2019
>  CMD: cd /var/log/apache && rm -f error_log && ln -s $(ls -r *error_log.* | head -1) error_log
>  root 12318 c Fri Apr 19 00:27:00 2019
<  root 12318 c Fri Apr 19 00:27:00 2019 rc=2
>  CMD: cd /var/log/apache && rm -f error_log && ln -s $(ls -r *error_log.* | head -1) error_log
>  root 13871 c Fri Apr 19 00:28:00 2019
<  root 13871 c Fri Apr 19 00:28:00 2019 rc=2
>  CMD: cd /var/log/apache && rm -f error_log && ln -s $(ls -r *error_log.* | head -1) error_log
>  root 23263 c Fri Apr 19 00:31:00 2019
<  root 23263 c Fri Apr 19 00:31:00 2019 rc=2
>  CMD: date>/tmp/date.out
>  root 25056 c Fri Apr 19 00:32:00 2019
<  root 25056 c Fri Apr 19 00:32:00 2019
^C
You have new mail in /var/mail/root
-bash-3.2# ls -l /tmp/date.out
-rw-r--r--   1 root     root          29 Apr 19 00:32 /tmp/date.out
-bash-3.2#

Not sure if "rc=2" is giving some indication

Last edited by solaris_1977; 04-19-2019 at 05:49 AM..
# 13  
It certainly does and might be listed in the Solaris documentation, to which I have no access. cron jobs send their output - if any - by mail. You seem to have received mail(s). What do they say? You might want to add some debug info to your commands - intersperse some echoes.
# 14  
rc=2 means exit status 2.
Quote:
You have new mail in /var/mail/root
Look at root's mail with
Quote:
tail -200 /var/mail/root

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