Matteo Riva's questions

If I understand correctly, when I do an incremental backup and a file has been removed from the client, the server marks it as inactive which makes it eligible for purging when the expire time has passed.

Using the dsmc client on a linux server I can see the list of inactive files, but no information is shown on how long they will be kept.

How can I know exactly when a specific inactive file will expire? Also: where do I configure the expire time and how do I see which value it is currently set to?

I am in the process of migrating everything from server A to server B and that includes email services.

I have already set up server B to accept mail for our domain, user authentication is working and I also have a script which runs an rsync of Maildir data from server A to server B making the needed changes to accomodate for dovecot. Mail delivery for another test domain configured on server B works fine.

My problem now is how to sync & switch from server B to server A without (if possible) having mail delivered to both server while DNS caches expire.

Is there a way I can avoid the "inconsistency" period due to DNS TTL and have a seamless switchover to the new server?

I noticed an error in google webmaster tools regarding a gzipped version of a sitemap. Turns out the sitemap.xml.gz file is gzipped twice: one upon creation (as it should be) and another time when being served.

The .htaccess file has this rule

AddOutputFilterByType DEFLATE application/xml

which I thought wouldn't match a gzipped XML file, but apparently it does as removing this solves the problem.

What am I doing wrong?

I have troubles understanding what problems may cause the occasional hangs that the server gets due to sudden high load spikes. I am not a system administrator (I'm a PHP programmer) but since the official sysadmin is quite lacking on effort I'm asked to find a solution myself.

The server runs on a Debian Lenny and serves via apache a wordpress + vbulletin based site with 40-60k visits/day. Having done all the application-side optimization I could, we got to the situation where the site runs smoothly even for weeks, then it trips on something that makes the server load jump up to 80+. Stopping apache to restart it helps, but it usually calms down by itself, if given enough time. It can "crash" twice in a day, or see no problems for weeks. It seems to be totally random.

One weird specific thing happened though. I was warned of a strange behavior and after inspection I found the .htaccess file changed to redirect traffic coming from search engines to some external site. I checked the code and every plugin (all up to date) and finally tried the "hard way" chowning .htaccess to root.root. The weird part is that when another issue came up, I found that file changed back to be owned by the user assigned to the website virtualhost. I understand there is no way for this to happen just via some web exploit, or am I mistaken?

How can I find the cause of this high load spikes?
What can explain a root.root file changing permissions, other that someone with root access doing it?
Could these two things be linked to some kind of attack?

I need to find a solution for a website which is struggling under load. The site gets ~500 simultaneous connections during peak time, and counts around 42k hits per day.

It's a wordpress based site bridged with a vbulletin forum with a lot of contents and a fairly complex structure which makes intensive use of the database. I already implemented code level full page caching (without this the server just crashes), and configured all other caching directives as well as combining css files and the like to limit http requests as much as possible.

I need to understand if there is more that can be done via software or if the load is just too much for the server to handle and it needs to be upgraded, because the server goes down occasionally during peak times.

Can't access the server now, but it's a dedicated CentOS machine (I think 4GB ram, can't say what CPU) running apache/mysql.

So back to the main question: how can I know when the users are just too many?

EDIT

I got access to the logs, according to error.log during yesterday's down it was apache segfaulting:

[Mon Apr 19 18:26:51 2010] [notice] child pid 4825 exit signal Segmentation fault (11)
[Mon Apr 19 18:26:53 2010] [notice] child pid 4794 exit signal Segmentation fault (11)
[Mon Apr 19 18:27:08 2010] [notice] child pid 4595 exit signal Segmentation fault (11)
[Mon Apr 19 18:27:11 2010] [notice] child pid 4826 exit signal Segmentation fault (11)
.....

How can I tell what's the cause of this segfault?

When I ask the server for an URL which has no extension, but is not a directory, apache automatically adds a .php extension to it. Where is this behavior configured?

EDIT: I'm sorry, my question wasn't clear: I'm not asking how to do this, I just found out that my local server (Apache/2.2.11 on Debian) does it by itself (i.e. I have no rewrite rules) and I wanted to know where this can be configured.

I don't know what else to check, I reinstalled wp-super-cache 0.9.7 following every line of the instrucions, activated by the admin page but nothing gets actually cached.

• I double checked .htaccess files in both document root and cache directory
• All directory permissions are granted to the webserver user
• WP_CACHE constant is defined to true
• PHP safe mode is disabled

What else can I do to finally get this plugin working?

Thanks