Tag Archives: sysadmin

Swappiness in linux

Leave a reply

Shamelessly stolen from wikipedia because they’re thinking about removing this, as  “Wikipedia is not a howto”. *sigh*.

 

With kernel version 3.5 and over, as well as kernel version 2.6.32-303 and over, it is likely better to use 1 for cases where 0 used to be optimal.

To temporarily set the swappiness in Linux, write the desired value (e.g. 10) to /proc/sys/vm/swappiness using the following command, running as root user:

# Set the swappiness value as root
echo 10 > /proc/sys/vm/swappiness

# Alternatively, run this
sysctl -w vm.swappiness=10

# Verify the change
cat /proc/sys/vm/swappiness
10

# Alternatively, verify the change
sysctl vm.swappiness
vm.swappiness = 10

Permanent changes are made in /etc/sysctl.conf via the following configuration line (inserted, if not present):

vm.swappiness = 10

10 is generally good for ‘I don’t want swapping to happen except if you *really* need it.

 

Varnish weird error

Leave a reply

Are you getting a weird error from varnish that you’re having trouble working out? Is it cryptically saying that there’s an issue with your host definition in your VCL?

Expected ID got ';'
 (program line 165), at
 ('input' Line 20 Pos 30)
 .first_byte_timeout = 120;
 -----------------------------#

You need to add a time unit to your timeout definitions — ‘s’ for seconds, ‘m’ for minutes.  Stupid cryptic error is dumbly cryptic. Grrr.
https://varnish-cache.org/lists/pipermail/varnish-bugs/2011-August/003983.html

ARGH! A Rant about software developers

1 Reply

When software developers update their software to include new configuration options, they have a bunch of options to pick from, of how to handle installs running on the old options.

For example, you could

  1.  automatically update config
  2.  document a process to gracefully update config
  3.  Give human readable errors showing what changes you need to make to conifg
  4.  Break the application with a super cryptic error message, and refuse to start until config is wiped with ‘new’ default config.

…

Why do developers keep picking 4? At least 2 horribly complex bits of software in the past year have decided to do that to me, which cost me a few days of head-bashing-against-desk trying to work out what was broken time. 🙁

Varnish nsca logging on systemd system with x-forwarded-for

Leave a reply

So, you have a Varnish server running systemd, which is behind a reverse proxy for SSL like nginx, and you can’t work out how to make varnishncsa log IP addresses from a specified header? Well, it’s a bit of a pain in the neck really. You need to override the systemd service file, which is like systemd’s version of the init scripts. Due to it being systemd, this is not just a case of editing a file…

For Debian, you can use the service file below, and paste it into
/etc/systemd/system/varnishncsa.service

Once done, you need to reload systemd’s service listing itself;
$ systemctl daemon-reload

Congratulations, you now have varnishncsa logs including the visitor’s real IP address, as specified by Nginx. Change the name in “{X-Forwarded-For}” to change the header name, for example if you want CloudFlare’s view of the client’s IP address, use “CF-Connecting-IP”

[Service]
 RuntimeDirectory=varnishncsa
 Type=forking
 PIDFile=/run/varnishncsa/varnishncsa.pid
 User=varnishlog
 Group=varnish
 ExecStart=/usr/bin/varnishncsa -a -w /var/log/varnish/varnishncsa.log -D -P /run/varnishncsa/varnishncsa.pid -F '%%{X-Forwarded-For}i %%l %%u %%t "%%r" %%s %%b "%%{Referer}i" "%%{User-agent}i"'
 ExecReload=/bin/kill -HUP $MAINPID

 

Find Windows workstation logon script

Leave a reply

This is a super quick tip from an online forum…
[Sevenforums.com: Where is the location for the windows logon script?]

If you’re looking for the location of the active logon script in a Windows domain network on a workstation, or just to figure out which logon script is being used for a workstation

TLDR; ‘Get to the point, where is the bleeding thing?!’:

To find the location of a user’s logon script, while logged in as the user, run the command:
net user “%USERNAME%” | find “Logon script”
or for a domain user,
net user “%USERNAME%” /domain | find “Logon script”

Standard location

The logon scripts themselves can be found on the network in the standard domain network share location:

\\%USERDOMAIN%\netlogon

Additionally, the commands:

net user “%USERNAME%” /domain

and

gpresult /r

Give interesting results for the current user and what Group policy rules are active for the currently logged in user/(machine?) respectively.

Obviously this is only relevant to windows computers in active directory with primary domain controller and group policy ordaining that each machine should run a logon script.

 

Search Terms:

Things i searched for in order to try and find this out:

  • find out what logon script a computer is using
  • find path of logon script from workstation
  • find path of logon script from workstation registry

(I couldn’t find the registry location as it turns out!)

If this post helped you, or you have additional tips, please leave them in the comments!

Odd Magento / Fishpig / WordPress error

8 Replies

If you get an error like:
Fatal error: Call to a member function select() on a non-object in /home/username/public_html/app/code/community/Fishpig/Wordpress/Model/Resource/Page.php on line 119

Then, check you’ve not just changed a MySQL username, without updating the fishpig configuration, or otherwise Fishpig can’t access the MySQL database for some reason. It seems to store a MySQL login in Magento config. I’ve not yet found exactly where, I’ll update this post with more once I understand more about what it’s doing.

 

It presented as the main Magento site throwing the following error:

exception ‘Zend_Exception’ with message ‘dbModel read resource does not implement Zend_Db_Adapter_Abstract’

 

Which it seems that most everyone will tell you to clear your cache to fix. You *will* need to clear your cache, probably. Just, after fixing the MySQL connection issue.

 

The following line is to make it easier for people googling to find this post:
Fatal error: Call to a member function select() on a non-object in /public_html/app/code/community/Fishpig/Wordpress/Model/Resource/Page.php on line 119 magento fishpig

 

This post my making sure  https://xkcd.com/979/ doesn’t happen from me.

grub-probe: error: no such disk

4 Replies

Ran into this one today, on a debian squeeze box:

/usr/sbin/grub-probe: error: no such disk.

It actually was telling the truth, the disks listed in /boot/grub/device.map were wrong. Replaced /dev/disk/by-id/serial-of-drive with /dev/sda. Worked.

Whilst researching this problem, I did run into a similar debian bug, but it wasn’t relevant. In case you’re interested, it’s about LVM drives, and it’s here: http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=673573

MySQL Linux CLI command execution

Leave a reply

As another aid to my memory, you can run mysql commands on the command line like this:

mysql -u user -p[password] database -e "SELECT * FROM orders;".

 

You can also send the mysql client commands on stdin:

echo "SELECT * FROM orders" | mysql -u user -p[password] database

 

Or read them in with a file redirection

mysql -u user -p[password] database < /home/kirrus/orders.sql

That last one is really handy for reading MySQL dumps back into MySQL.