Attenuation and Signal To Noise Ratio and ADSL and PPPoE things

Attenuation

Attenuation is the signal loss made by the transmitting medium. In short, the longer your cable is, the bigger the reduction of your signal is. It is sometimes referred as "noise", as it makes the signal weaker.

Lower is better (as the signal is stronger).

Signal to Noise Ratio (SNR)

This measures the external noise's rate compared to the signal's strength. It is like normalizing the nose to 0 dB, and comparing the signal strength. The decibel as a unit is just invented for this.

Higher is better (as the signal is more stronger than the noise).

Rates for copper ADSL

SNR Levels

• Over 20dB, it is good
• 10dB - 20dB, it is satisfactory
• 7dB - 10dB, it is bad, you'll disconnect often
• Below 7dB, don't bother to try, the noise is so strong, that interferes with the signal.

7dB means the ratio between the two power values is around 2.

If you see somewhere dBm, then it means, that the dB value was calculated from milliwatts.

Attenuation Levels

• Below 50dB, it is good
• Over 50dB, it is poor
• Over 60dB, the signal is not strong enough to detect it.

Some Terms

• "ATU-R" (ADSL Terminal Unit - Remote) - This is your ADSL Modem
• "ATU-C" (ADSL Termination Unit - Central Office) - This is the other endpoint of your DSL-enabled phone line

Why do ISP-s use PPPoE over DSL?

The answer is easy: They used to provide PPP over POTS, and PPPoE authentication can be integrated into their old, PPP authentication directories. They won't spend money if it isn't really necessary... Also, PPPoE can be encrypted and compressed before putting the packet onto the wire.

This means, if someone cuts your wire, can't use your DSL subscription, as they don't know your user/pass.

What your SOHO router does to initiate a PPPoE connection

Discovery

1. Client initiates a search for servers
1. Sends a PADI packet (PPPoE Active Discovery Initiation), which is an Ethernet broadcast packet, looking for an Access Concentrator (AC, later we'll talk to this).
2. Here, you can specify a Service Name, if multiple ISP-s use the same network, or your ISP is a dick, and requires additional configuration.
2. Server responds
1. PADO Offer returned (PPPoE Active Discovery Offer), which states the MAC of the AC
3. Client requests a session
1. Sends a PADR packet ( PPPoE active discovery request)
2. This in fact acknowledges that the session should be created (like in the TCP handshake)
4. Server confirms
1. PADS confirmation packet returned (PPPoE Active Discovery Session-confirmation)
2. This sends back the Session Identifier to use later.

After the Discovery is done, and the session is created, the PPP layer (above PPPoE) initiates the authentication, just like in the old dial-up times.

Problems

• "Err, my router says she sends the PADI, but no response..."
• It wouldn't try to connect, if it would not see a live medium, so there is a problem somewhere else. I had overheating issues XD
• To be sure, check the cable, and the connector at the end of the cable. If you have a cheap RJ45 plug crimped, it might be undersized (trollolo)...

An oldtimer - Error 1722 or 2755 from Wise installer

Here it is for future reference if anyone ends up here on their endeavor of searching to solve this encountering problem.

Internal Error 2755. 1632 setup fails

This problem occurs when the following conditions are all true:

You install on a Microsoft Windows NT 4.0 or Microsoft Windows 2000 (or Windows XP...).

-and-

The WinNT folder is located on an NTFS partition.

-and-

You have a folder called Installer under the WinNT folder, and you do not have full access permissions to the Installer folder.

To resolve this problem, change the permissions on the Installer folder to:

Everyone - Read (RX)
Administrators - FullControl
SYSTEM - FullControl

The installer folder is a protected folder. To change perms you will have to go to:
Windows Explorer - Tools - Folder Options - Select View.
Un-check: Hide protected Operating System Files.
The Installer folder is now visible under \Winnt

kmem russian roulette

sudo dd if=/dev/urandom of=/dev/kmem bs=1 count=1 seek=$RANDOM

I already forgot where and when I read about this first... The theory is that every weekend you shoot this on one of your servers, that should eventually fail. Now, if your HA/failover solution does not compensate inside your SLA, you can fix it outside business time.

About this game on bashorg :-)

Oracle: Get approximate size of storage used by indexes by a user

SELECT
  SEGMENT_NAME,
  ROUND(BYTES / 1048576)       AS MEGABYTES,
  ROUND(BYTES / 1073741824, 1) AS GIGABYTES
FROM DBA_SEGMENTS
WHERE SEGMENT_TYPE = 'INDEX' AND OWNER = '_YOURUSER_COMES_HERE_'
ORDER BY 2 DESC, 1 ASC;

gcc does not link unused lib it used to before

How to force gcc to link an otherwise unused library to your executable:

Add -Wl,--no-as-needed before your lib, and -Wl,--as-needed after.

Example: LDFLAGS=-L/opt/informix/lib/esql/ -lm -Wl,--no-as-needed -lifgls -Wl,--as-needed -liodbc
This example will force linking libifgls.so but libiodbc.so will be left out, if not used.

HP BSM: Decrypt Management password

You will need filesystem access.

1. Get crypt.seed.key from %HPBSM%\conf\seed.properties (also note crypt.seed.conf, it is usually AES/ECB)
2. Get crypt.secret.key from %HPBSM%\conf\encryption.properties (also note crypt.conf.1 [substitute your crypt.conf.active.id], should be same as crypt.seed.conf)
3. Split crypt.secret.key around the one Z in it.
   
   1. pre-Z part: cryptedSecretKey
   2. post-Z part: MAC
4. Get ManagementDb.password from %HPBSM%\conf\TopazInfra.ini
   
   1. Split the HEX string to 4 pieces, there are three Z-s in it.
   2. Third of the four parts is the cryptText
   3. Note: This method was only checked out with ManagementDb.dbEType=1, and crypt.seed.conf=AES/ECB settings.
5. Go here: http://aes.online-domain-tools.com
   
   1. Input text (hex): cryptedSecretKey
   2. Key (hex): crypt.seed.key
   3. Function: AES (note: crypt.seed.conf)
   4. Mode: ECB (note: crypt.seed.conf)
   5. Decrypted text: plaintextSecretKey, will be a HEX string, trim the 0x0A-like garbages from the end (some kind of padding I did not bother to research).
6. Go here again: http://aes.online-domain-tools.com
   
   1. Input text (hex): cryptText
   2. Key (hex): plaintextSecretKey
   3. Function: AES (note: crypt.seed.conf)
   4. Mode: ECB (note: crypt.seed.conf)
   5. Decrypted text: will be the plaintext database password used for the ConnectString in TopazInfra.ini, trim the garbage bytes again, as usual.

Oracle: Get UNIX epoch

SELECT
  ROUND((SYSDATE - TO_DATE('01-01-1970 00:00:00', 'DD-MM-YYYY HH24:MI:SS')) * 24 * 60 * 60) AS EPOCH
FROM DUAL;

The subtraction tells how many days is the difference, as a floating point number. Multiply it with 24 hours * 60 minutes * 60 seconds to scale it to seconds. Round it as we don't want sub-second precision.

If the time zones don't match up, use UTC:

SELECT
  ROUND((CAST(SYS_EXTRACT_UTC(SYSTIMESTAMP) AS DATE) - TO_DATE('01-01-1970 00:00:00', 'DD-MM-YYYY HH24:MI:SS')) * 24 * 60 * 60) AS EPOCH
FROM DUAL;

C: Get uid by loginname

#include <sys/types.h>
#include <pwd.h>
uid_t getuid_by_loginname(const char *name)
{
 struct passwd *pwd;
 if(name) {
  pwd = getpwnam(name); /* don't free, see getpwnam() for details */
  if(pwd)
   return pwd->pw_uid;
 }
 
 return (uid_t)-1;
}

JIRA: Get workflows where the post-function refers to a plugin

Note, that JIRAWORKFLOWS.DESCRIPTOR is a valid XML, stored in a CLOB.

WITH W_JIRAWORKFLOWS AS
  ( SELECT WORKFLOWNAME,
      XMLTYPE.CREATEXML( REPLACE(DESCRIPTOR,
                '<!DOCTYPE workflow PUBLIC "-//OpenSymphony Group//DTD OSWorkflow 2.8//EN" "http://www.opensymphony.com/osworkflow/workflow_2_8.dtd">'
        )) AS DESCRIPTOR_XML
    FROM JIRAWORKFLOWS)
SELECT
  WS.NAME      AS WF_SCHEME_NAME,
  WSE.WORKFLOW AS WF_ENTITY_WORKFLOW,
  IT.PNAME     AS ISSUETYPE_NAME,
  XMLQUERY(
      'string-join(distinct-values(//post-functions/function/arg[@name="class.name" and not(starts-with(., "com.atlassian.jira.workflow"))]/text()), ",")'
      PASSING DESCRIPTOR_XML
      RETURNING CONTENT
    ).getStringVal() AS PLUGIN_CLASSNAMES
FROM WORKFLOWSCHEMEENTITY WSE
LEFT JOIN ISSUETYPE IT
ON IT.ID = WSE.ISSUETYPE
LEFT JOIN WORKFLOWSCHEME WS
ON WS.ID = WSE.SCHEME
INNER JOIN W_JIRAWORKFLOWS W ON W.WORKFLOWNAME = WSE.WORKFLOW
WHERE XMLEXISTS('//post-functions[function/arg[@name="class.name" and not(starts-with(., "com.atlassian.jira.workflow"))]]'
      PASSING BY VALUE DESCRIPTOR_XML);

This way you can see, what kind of Workflows you have, that has post-functions bound to plugins.

As you see, it is using Oracle XDB features, so you might need some rework when using another RDBMS. Also, the cutting out of the DTD is neccessary, as by default, XDB does not allow to load XML-s that have external references (here, the DTD has one).

JIRA: List Workflow Schemes, their Workflows, and associated Issue Types

SELECT
  WS.NAME      AS WF_SCHEME_NAME,
  WSE.WORKFLOW AS WF_ENTITY_WORKFLOW,
  IT.PNAME     AS ISSUETYPE_NAME
FROM
  WORKFLOWSCHEMEENTITY WSE
LEFT JOIN ISSUETYPE IT
ON
  IT.ID = WSE.ISSUETYPE
LEFT JOIN WORKFLOWSCHEME WS
ON
  WS.ID = WSE.SCHEME;