All Questions(server)

I'm experiencing 502 Gateway errors when accessing a PHP file in a directory (http://example.com/dev/index.php). The logs simply says this:

2011/09/30 23:47:54 [error] 31160#0: *35 connect() failed (111: Connection refused) while connecting to upstream, client: xx.xx.xx.xx, server: domain.com, request: "GET /dev/ HTTP/1.1", upstream: "fastcgi://127.0.0.1:9000", host: "domain.com"

I've never experienced this before. What is the solution for this type of 502 Gateway error?

This is the nginx.conf:

user www-data;
worker_processes 4;
pid /var/run/nginx.pid;

events {
    worker_connections 768;
    # multi_accept on;
}

http {

    ##
    # Basic Settings
    ##

    sendfile on;
    tcp_nopush on;
    tcp_nodelay on;
    keepalive_timeout 65;
    types_hash_max_size 2048;
    # server_tokens off;

    # server_names_hash_bucket_size 64;
    # server_name_in_redirect off;

    include /etc/nginx/mime.types;
    default_type application/octet-stream;

    ##
    # Logging Settings
    ##

    access_log /var/log/nginx/access.log;
    error_log /var/log/nginx/error.log;

    ##
    # Gzip Settings
    ##

    gzip on;
    gzip_disable "msie6";

    # gzip_vary on;
    # gzip_proxied any;
    # gzip_comp_level 6;
    # gzip_buffers 16 8k;
    # gzip_http_version 1.1;
    # gzip_types text/plain text/css application/json application/x-javascript text/xml application/xml application/xml+rss text/javascript;

    ##
    # Virtual Host Configs
    ##

    include /etc/nginx/conf.d/*.conf;
    include /etc/nginx/sites-enabled/*;
}

Can anyone clarify the differences between the --checksum and --ignore-times options of rsync?

My understanding is as follows:

--checksum
If the file size and time match, it will do a checksum at both ends to see if the files are really identical.

--ignore-times
'Transfer' every file, regardless of whether file time is same at both ends. Since it will still use the delta-transfer algorithm, if a file actually is identical, nothing gets transferred.

That's the technical difference, but as far as I can tell, they are semantically the same thing.

So, what I'm wondering is:

• What is the practical difference between the two options?
• In what cases would you use one rather than the other?
• Is there any performance difference between them?

I would like to see the Time-To-Live (TTL) value for a CNAME record.

I have access to dig (on Apple Mac OS X), which gives me an answer like this:

% dig host.example.gov
<*SNIP*>
;; ANSWER SECTION:
host.example.gov.       43200   IN  CNAME   host1.example.gov.
host1.example.gov.      43200   IN  A       192.168.16.10

Is the value '43200' the TTL for this DNS record?

I need to write some complex xml to a variable inside a bash script. The xml needs to be readable inside the bash script as this is where the xml fragment will live, it's not being read from another file or source.

So my question is this if I have a long string which I want to be human readable inside my bash script what is the best way to go about it?

Ideally I want:

• to not have to escape any of the characters
• have it break across multiple lines making it human readable
• keep it's indentation

Can this be done with EOF or something, could anyone give me an example?

e.g.

String = <<EOF
 <?xml version="1.0" encoding='UTF-8'?>
 <painting>
   <img src="madonna.jpg" alt='Foligno Madonna, by Raphael'/>
   <caption>This is Raphael's "Foligno" Madonna, painted in
   <date>1511</date>-<date>1512</date>.</caption>
 </painting>
EOF

When someone mentions RAID in a conversation about backups, invariably someone declares that "RAID is not a backup."

Sure, for striping, that's true. But what's the difference between redundancy and a backup?