Ever been on a machine that was ailing and just wouldn't respond? As soon as you're root, lower the priority of the offending process ID(s) (in this example, 1103) by using the 'renice' command:

# renice -19 1103

If you want to view your PAT for debugging:

pixfirewall# show xlate debug

When you're doing a packet capture for the purpose of examining the frame payload, you'll want to extend the snaplen (snapshot length) to 1515. That's long enough to accomodate the 1500 MTU and should give you a pretty good look at what you're after.

For example:

# tcpdump -s1515 -X -ieth0 -w sample.cap

Note: This applies to 'ethereal' and 'wireshark' but their defaults are to capture max(INT) by default.

If you've munged your template1 database, you can rebuild it from the template0 database.

First, you must set the datistemplate attribute of template1 to false so we can drop it:

xinu=# UPDATE pg_database SET datistemplate = false WHERE datname = 'template1';
UPDATE 1
xinu=# DROP DATABASE template1;
DROP DATABASE

Next, re-create template1 using template0 as a template:

xinu=# CREATE DATABASE template1 WITH TEMPLATE = template0;
CREATE DATABASE

Then restore the datistemplate attribute of template1:

xinu=# UPDATE pg_database SET datistemplate = true WHERE datname = 'template1';
UPDATE 1

If you see the following when trying to load a newly transplanted database, it may be due to a difference in architecture (32-bit vs. 64-bit):

FATAL:  incorrect checksum in control file.

The moral is: never do a direct copy of the data directory. It isn't considered good practice.

You can use the lsof (LiSt Open Files) utility to view information about which processes own file handles on a system. Since sockets map to file descriptors, lsof will show you which processes own socket connections. If you see that your machine is connected to another on TCP port 6234 (source or dest) and you want to find out which process(es) are responsible for the connection, run:

# lsof -ni tcp:6234

Note that when run as an unprivileged user, lsof will only show you file descriptors that you have permission to see. You must run lsof as root to see everything in the kernel.

You can use this query to find the table information:

SELECT
  a.attnum,
  a.attname AS field,
  t.typname AS type,
  a.attlen AS length,
  a.atttypmod AS lengthvar,
  a.attnotnull AS notnull
FROM
  pg_class c,
  pg_attribute a,
  pg_type t
WHERE
  c.relname = 'your_table_name'
  AND a.attnum > 0
  AND a.attrelid = c.oid
  AND a.atttypid = t.oid
  ORDER BY a.attnum

If you want to see how long a query is taking to run, you can either run explain analyze or enable timing for the client by typing \timing.

You can use the tee program to save the contents of a pipe to a file while also viewing it on standard out:

# tail -0f /var/log/httpd/error_log | tee ~/newest_errors.txt

Note: tail -0 instructs tail to begin at the very end of the file (the default is to show the last ten lines), and -f means tail will periodically check the file for additional data and print the data to standard out.

Set this variable in your ~/.psqlrc to stop on error when psql is used to run non-interactive scripts (e.g. cat file | psql ...):

\set ON_ERROR_STOP 1

Or use it from the command line:

$ psql ... -v ON_ERROR_STOP=1 ...

Netcat is handy little utility for scripting all manners of network functionality. Here we're making sure a web server is responding as we'd expect:

$ (echo "GET / HTTP/1.1"; echo "Host: www.xinu.org"; echo) | nc www.xinu.org 80

If you have a database mytemplate that you'd like to use as a template, update its datistemplate attribute in the pg_database relation:

UPDATE pg_database SET datistemplate = 't' WHERE datname = 'mytemplate';

Then you can use it as a template when creating other databases:

CREATE DATABASE otherdb TEMPLATE mytemplate;

Due to the checksum offloading logic that's built into most current NICs you'll sometimes get several TCP checksum errors in your Wireshark packet captures. To prevent this, you can go into Edit > Preferences and choose TCP in the left frame. In the right frame, un-check 'Validate the checksum if possible'.