RJ-45自製網路線

測線器,一個發射端,一個接收端,上面8顆燈號

發射端會依序打出信號 1~8號燈,然後看接收器 1~8號燈 有沒有亮。

沒亮 = 線材中間斷蕊

亮的燈號順序不對 = 壓頭蕊線顏色排列錯誤,重壓

rj45

rj45-2

Reference: http://blog.xuite.net/axian/blog/224348022-%E8%87%AA%E5%B7%B1%E5%8B%95%E6%89%8B+DIY+RJ45+%E7%B6%B2%E8%B7%AF%E7%B7%9A%E6%8E%A5%E9%A0%AD%E5%90%A7%EF%BC%81

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Mac: Reset home folder permissions

This is for Mountain Lion.

http://www.fixkb.com/2011/08/reset-home-folder-permissions.html

  1. In Terminal, type sudo bash and press Enter.
  2. You will need to enter your password and press Enter.
    • It won’t show any characters when you type.
    • If you do not have a password then set one first.
  3. Type in the following (case-sensitive), pressing Enter at the end of each line.
    Replace “username” with the name of your home folder.
    sudo chmod -R -v -N ~
    sudo chown -R username:staff ~
    sudo chmod -R -v 700 ~
    sudo chmod -v 755 ~

MySQL 5.x Repair Cheat Sheet

If you upgrade MySQL or move the database around, you are most likely need to do those operations:

Backup

mysqldump -u root -p --default-character-set=utf8 databasename > data.sql

Restore

mysqldump -u root -p --default-character-set=utf8 databasename < data.sql
if database is larger then 100MB, this works better:
mysql -u root -p
#mysql> use the_database
#mysql> source data.sql

Check, Repair & Optimize All Tables in All Databases

If you need database server up, use mysqlcheck:
mysqlcheck -u root -p --auto-repair --check --optimize --all-databases

Or you can make it offline and do a better check:
service mysqld stop
myisamchk /var/lib/mysql/the_database/*.MYI
service mysqld start

Repair single table

mysql -u root -p
#mysql> use the_database
#mysql> repair table the_table

Reference:
http://www.felipecruz.com/repair-mysql-database.php

CentOS – Install latest PHP (5.2.x) from Remi repository

A few app requires PHP 5.2.x but major repositories is yet support anything higher than 5.1.6 at this time. Recompile PHP is a pain also.

Remi maintains a repository that can save your 1 day or 2 if you have such need.

cd /etc/yum.repos.d/
wget http://download.fedora.redhat.com/pub/epel/5/i386/epel-release-5-3.noarch.rpm
wget http://rpms.famillecollet.com/enterprise/remi-release-5.rpm
rpm -Uvh remi-release-5*.rpm epel-release-5*.rpm

You now have Remi repository on your system. It’s disabled by default, and I recommend you leave it as is. To install from remi, run the following:

yum --enablerepo=remi update php

I use remi to install php and its related stuff like GD, mcrypt, etc. As well as MySQL. The repository rocks!

Recover a disk failure for LVM (CentOS)

I’ve put together old hardware pieces at home for a download & file sharing box. It got 4 old disks (30G, 250G, 500G, 80G) together. Knowing that disks will out of its life sooner or later, I rsync important stuff to the mac next to it. Couple weeks ago, shit finally happen.

The broken disk is the 30G, so most of stuff are still in the other disks. To recover, I put into a new disk, re-install CentOS, so the box is bootable again. Now I need to re-activate and mount the old disks.

Re-install CentOS
1.Put in the new disk, go to Bios and make sure CD-ROM is having first boot priority, and the new disk is the boot disk in Hard Disk boot priority setting.
2.Put in the CentOS DVD, boot from it. In the install process, make sure you don’t re-partition the old disks.
3.If you are not sure what to do, you can un-plug the power cores of all old disks, install on the new disk first. Once the installation is finished, plug back the power of old disks, boot from DVD again, and reset the boot loader.
4.Now you’ve got a bootable box with all the disks in place.

RHEL systems like Red Hat, CentOS or Fedora, partition the disks automatically at install time. By default, it sets up the partitions using LVM for the root device.
By default, the OS set up a volume group called VolGroup00, with two logical volumes, LogVol00 and LogVol01, the first for the root directory and the second for swap.

Since the new disk is big enough, I set up the new disk (not using the volume). As you can see in the partition layout of physical disks below (/dev/sda is the new disk):
[root@xxx]# sfdisk -l

Disk /dev/hda: 19457 cylinders, 255 heads, 63 sectors/track
Units = cylinders of 8225280 bytes, blocks of 1024 bytes, counting from 0

Device Boot Start End #cyls #blocks Id System
/dev/hda1 * 0+ 19456 19457- 156288321 8e Linux LVM
/dev/hda2 0 - 0 0 0 Empty
/dev/hda3 0 - 0 0 0 Empty
/dev/hda4 0 - 0 0 0 Empty

Disk /dev/hdc: 24792 cylinders, 255 heads, 63 sectors/track
Units = cylinders of 8225280 bytes, blocks of 1024 bytes, counting from 0

Device Boot Start End #cyls #blocks Id System
/dev/hdc1 * 0+ 24791 24792- 199141708+ 8e Linux LVM
/dev/hdc2 0 - 0 0 0 Empty
/dev/hdc3 0 - 0 0 0 Empty
/dev/hdc4 0 - 0 0 0 Empty

Disk /dev/sda: 38913 cylinders, 255 heads, 63 sectors/track
Units = cylinders of 8225280 bytes, blocks of 1024 bytes, counting from 0

Device Boot Start End #cyls #blocks Id System
/dev/sda1 * 0+ 12 13- 104391 83 Linux
/dev/sda2 267 38912 38646 310423995 83 Linux
/dev/sda3 13 266 254 2040255 82 Linux swap / Solaris
/dev/sda4 0 - 0 0 0 Empty

Disk /dev/sdb: 60801 cylinders, 255 heads, 63 sectors/track
Units = cylinders of 8225280 bytes, blocks of 1024 bytes, counting from 0

Device Boot Start End #cyls #blocks Id System
/dev/sdb1 * 0+ 60800 60801- 488384001 8e Linux LVM
/dev/sdb2 0 - 0 0 0 Empty
/dev/sdb3 0 - 0 0 0 Empty
/dev/sdb4 0 - 0 0 0 Empty

To re-activate and re-mount
vgchange is the utility to update/change your volume group attribute. Since one of the disk in previous volume is missing, I need to vgchange –ay –partial to activate the volume.

[root@xxx]# vgchange –ay –partial
Couldn't find device with uuid 'AiegxE-NfQy-AA5E-OUcn-bvpY-UG3o-5oT1gY'.
/dev/mapper/VolGroup00-LogVol00-missing_3_0: read failed after 0 of 4096 at 0: Input/output error
/dev/mapper/VolGroup00-LogVol01-missing_0_0: read failed after 0 of 4096 at 0: Input/output error
/dev/VolGroup00/LogVol01: read failed after 0 of 4096 at 0: Input/output error
Couldn't find device with uuid 'AiegxE-NfQy-AA5E-OUcn-bvpY-UG3o-5oT1gY'.
2 logical volume(s) in volume group "VolGroup00" now active

Well, a lot of error due to the missing disk, but the volume is active now. You can verify by:

[root@xxx]# lvscan
/dev/VolGroup00/LogVol00: read failed after 0 of 4096 at 892413607936: Input/output error
/dev/VolGroup00/LogVol00: read failed after 0 of 4096 at 892413665280: Input/output error
/dev/mapper/VolGroup00-LogVol01-missing_0_0: read failed after 0 of 4096 at 2080309248: Input/output error
/dev/mapper/VolGroup00-LogVol01-missing_0_0: read failed after 0 of 4096 at 4096: Input/output error
/dev/mapper/VolGroup00-LogVol01-missing_0_0: read failed after 0 of 4096 at 0: Input/output error
/dev/VolGroup00/LogVol01: read failed after 0 of 4096 at 2080309248: Input/output error
/dev/VolGroup00/LogVol01: read failed after 0 of 4096 at 2080366592: Input/output error
Couldn't find device with uuid 'AiegxE-NfQy-AA5E-OUcn-bvpY-UG3o-5oT1gY'.
/dev/mapper/VolGroup00-LogVol00-missing_3_0: read failed after 0 of 4096 at 0: Input/output error
/dev/VolGroup00/LogVol01: read failed after 0 of 4096 at 0: Input/output error
Couldn't find device with uuid 'AiegxE-NfQy-AA5E-OUcn-bvpY-UG3o-5oT1gY'.
/dev/mapper/VolGroup00-LogVol00-missing_3_0: read failed after 0 of 4096 at 0: Input/output error
/dev/VolGroup00/LogVol01: read failed after 0 of 4096 at 0: Input/output error
Couldn't find device with uuid 'AiegxE-NfQy-AA5E-OUcn-bvpY-UG3o-5oT1gY'.
ACTIVE '/dev/VolGroup00/LogVol00' [831.12 GB] inherit
ACTIVE '/dev/VolGroup00/LogVol01' [1.94 GB] inherit

Now you can mount the active volume by:
[root@xxx]# mount /dev/VolGroup00/LogVol00 /mnt

The old volume is now accessible at /mnt
[root@xxx]# ls –al /mnt

What Next
I copy the stuff I want to recover. What to do with the old drives? I need to think about…Having a old box on all time is actually costly (in term of electric bill). But having a box on is handy in many occurrences..

Ref:
http://www.linuxjournal.com/article/8874
http://fedoraforum.org/forum/archive/index.php/t-64964.html

Network Time (NTP) service in CentOS

Synchronize the clocks is standard now-da-day. If you don’t have NTP for some reason, here’s how you set it up in CentOS.

First Install the NTP Package on your server as root.

# yum install ntp
Loading “fastestmirror” plugin
Loading mirror speeds from cached hostfile
* base: mirror.steadfast.net
* updates: mirrors.liquidweb.com
* addons: pubmirrors.reflected.net
* extras: pubmirrors.reflected.net
Setting up Install Process
Parsing package install arguments
Resolving Dependencies
–> Running transaction check
—> Package ntp.i386 0:4.2.2p1-8.el5.centos.1 set to be updated
–> Finished Dependency Resolution

Dependencies Resolved

=================================================================
Package Arch Version Repository Size
=================================================================
Installing:
ntp i386 4.2.2p1-8.el5.centos.1 base 1.3 M

Transaction Summary
=================================================================
Install 1 Package(s)
Update 0 Package(s)
Remove 0 Package(s)

Total download size: 1.3 M
Is this ok [y/N]: y
Downloading Packages:
(1/1): ntp-4.2.2p1-8.el5. 100% |=========================| 1.3 MB 00:19
Running rpm_check_debug
Running Transaction Test
Finished Transaction Test
Transaction Test Succeeded
Running Transaction
Installing: ntp ######################### [1/1]

Installed: ntp.i386 0:4.2.2p1-8.el5.centos.1
Complete!

Next set it to start automatically on a reboot

# chkconfig ntpd on

Tell it which NTP server it should update it’s time from

# ntpdate pool.ntp.org
4 Aug 12:32:43 ntpdate[9540]: step time server 64.202.112.75 offset 1256.453048 sec

Verify that the Time & Date are correct

# date
Mon Aug 4 12:33:04 EDT 2008

Finally start the service

# service ntpd start
Starting ntpd: [ OK ]