Archive for the ‘Linux OS’ Category

Error: Your “crontab” on unexpected end of line. This entry has been ignored

January 20th, 2024, posted in Linux OS, Uncategorized
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Everytime you edit your crontabe file, the error “Your “crontab” on <server> unexpected end of line. This entry has been ignored” is sent to the users email. This happens if there is a blank line in your crontab file.


For instance, in the following crontab file there is a blank line between the last two cron jobs.

root@sunsolaris# crontab -l
# The root crontab should be used to perform accounting data collection.
#
# The rtc command is run to adjust the real time clock if and when
# daylight savings time changes.
#
10 1 * * 0,4 /etc/cron.d/logchecker
10 2 * * 0  /usr/lib/newsyslog
15 3 * * 0 /usr/lib/fs/nfs/nfsfind

30 4 * * * /usr/local/bin/disk_check,sh
;;;;
;;;
;;
;

To resolve the problem edit the crontab file and look for the blank line and delete the line. In the above, after editing the crontab, it should look lie the follows:

root@sunsolaris# crontab -l
# The root crontab should be used to perform accounting data collection.
#
# The rtc command is run to adjust the real time clock if and when
# daylight savings time changes.
#
10 1 * * 0,4 /etc/cron.d/logchecker
10 2 * * 0  /usr/lib/newsyslog
15 3 * * 0 /usr/lib/fs/nfs/nfsfind
30 4 * * * /usr/local/bin/disk_check,sh
;;;
;;
;

You can see the  blank line removed from the crontab file.

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Memory missing in Solaris 10 with ZFS

January 7th, 2024, posted in Solaris
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Ever wondered all the precious memory installed on your server has gone? Among many other reasons, if you are running Solaris 10 and use ZFS file system then there may be your answer.

ZFS Adaptive Replacement Cache (ARC) tends to use up to 75% of the installed physical memory on servers with 4GB or less and upto everything except 1GB of memory on servers with more than 4GB of memory to cache data in a bid to improve performance.

This can significantly affect performance on mission critical servers running Databases etc.

To identify how much memory uses:

# kstat -m zfs | grep size

        data_size                       18935877120
        hdr_size                        66041496
        l2_hdr_size                     0
        l2_size                         0
        other_size                      11310112
        size                            19013228728

Here “19013228728” (approx 18G) indicates the total memory used by ZFS.

Alternatively, the following mdb command show ZFS ARC usage:

# echo "::arc" | mdb -k|grep size
size                      =      2048 MB
hdr_size                  =  12493584
data_size                 = 2048608256
other_size                =  86475456
l2_size                   =         0
l2_hdr_size               =         0

It makes sense to cap the maximum ZFS ARC can use on servers where memory requirement for other services is more.

To set the maximum limit for ZFS ARC, edit /etc/system file and add the following line

set zfs:zfs_arc_max=2147483648

where 2147483648 restricts the usage to a maximum of 2GB physical memory. Unfortunately, this requires a reboot for the setting to take effect and cannot be dynamically changed.

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touch: cannot touch file No such file or directory  Alerting On Read Only Filesystem Errors

November 25th, 2023, posted in Linux OS
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Troubleshooting filesystem issues can be a complicated task, and it is made almost impossible if the system is unable to create logs or if you’re unable to access the logs.

There are few instances in which this might occur. This article will focus on a specific instance: when the file system is remounted as read-only.

Read-only Filesystem Issue / Errors

By default, Linux will mount the filesystems as read+write, but some times, due to failures, they can be automatically remounted as read-only. When that happens, well, you can only read your files, not write to them.

There a couple of different reasons why an issue like this might occur. One of the more common reasons is when the system boots after a crash (or loses power) where it is unable to shutdown correctly. The system will try to auto correct during boot, but if it is unable to do so, it will mount in read-only mode.

A real-world example might be if your hosting provider has an infrastructure failure. Your servers come online, but all of a sudden the file-system is in a read-only mode.

Working with Read-only Filesystem Logs

Building on the above scenario, let’s assume your server filesystem is in read-only mode. What do you do? How do you identify that is what is happening?

First, keep an eye out for “cannot create file: read-only file system” warnings in terminal. Such an example might occur if you try to do something like this:

root@test-server:~# tail /va-bash: cannot create temp file for here-document: Read-only file system
-bash: cannot create temp file for here-document: Read-only file system

This is a good indicator that a problem exists. A good way to confirm is by trying to touch a file to see if works:

root@test-server:~# touch test
touch: cannot touch 'test': Read-only file system

If it does not allow you to create the file you know where the issue is, you’re likely working a read-only file system issue.

Anther way to test is using mount. You can type the command “mount” and the output will give you something like this: , you can confirm if the server is in read-only (ro) mode:

# mount
..
/dev/sda4 on / type ext4 (ro,relatime,data=ordered)

In the entry above you see the reference to ro which is the abbreviation for read-only.

Solving the issue can be as simple as rebooting the server, but if that does not work you will have to investigate further.

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Free Hands On Practice Lab For Solaris 11

July 1st, 2023, posted in Solaris
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Hi, I was doing some researching on database migration from AIX and Solaris and I found some interesting stuff..

Oracle has provided some free lab session for new Solaris administrators to get their hands dirty..
If you are new to Unix and want to try them out, you can check out the links below !!

Just a side note, I came to know about Wintel environments, either  Oracle/MSSQL on Windows Server 2008/2012. It was a utter pain to work with the permissions and services. Unix/Linux is still better enterprise operating systems.

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