Good article

http://techtalk.vn/nhung-thoi-quen-xau-lam-kim-ham-su-tien-bo-cua-cac-lap-trinh-vien-moi-bat-dau-lam-chua-lau-ma-toi-da-nhan-ra-trong-khi-kem-cap-ho.html

https://medium.com/the-mission/40-things-about-life-i-wish-i-could-travel-back-in-time-and-tell-myself-e52f2effa3ab#.rs1x9oaih

https://khmt.wordpress.com/2016/08/22/mastering-programming/

Note Django

https://simpleisbetterthancomplex.com/2015/11/23/small-open-source-django-projects-to-get-started.html
https://python.web.id/blog/create-command-line-interfaces-with-python/

How to read source code

http://www.skorks.com/2010/05/why-i-love-reading-other-peoples-code-and-you-should-too/
http://wiki.c2.com/?TipsForReadingCode

Những thói quen xấu kìm hãm sự tiến bộ của lập trình viên

http://techtalk.vn/nhung-thoi-quen-xau-kim-ham-su-tien-bo-cua-lap-trinh-vien.html

Note Go

https://speakerdeck.com/mitchellh/advanced-testing-with-go
http://golanggo.com/archive
https://talks.golang.org/2016/applicative.slide#1
https://talks.golang.org/2014/organizeio.slide#1
https://talks.golang.org/2012/10things.slide#4
http://www.slideshare.net/InfoQ/experiences-building-influxdb-in-go
http://www.slideshare.net/InfoQ/beyond-the-hype-4-years-of-go-in-production
https://www.netlify.com/blog/2016/10/20/building-a-restful-api-in-go/
https://www.goinggo.net/2014/05/methods-interfaces-and-embedded-types.html

Some useful command

# lsmod
megaraid_sas           91199  26

# modinfo megaraid_sas

filename:       /lib/modules/3.13.0-92-generic/kernel/drivers/scsi/megaraid/megaraid_sas.ko

description:    LSI MegaRAID SAS Driver

author:         megaraidlinux@lsi.com

version:        06.700.06.00-rc1

# modinfo file.ko

# dpkg -c file.deb ( contains in deb )

# dpkg -x file.deb /tmp/file ( extract file in deb )

# dpkg -e file.deb ( extract control file, such as preinst, postinst, prerm, postrm )

Scan LVM partition

If your OS partition die, but data in other disks run LVM, you can reinstall OS and mount logical volume to use.

Example
# pvscan
  PV /dev/vdb   VG vgdata   lvm2 [20,00 GiB / 5,00 GiB free]
  Total: 1 [20,00 GiB] / in use: 1 [20,00 GiB] / in no VG: 0 [0   ]

# vgscan 

  Reading all physical volumes.  This may take a while...

  Found volume group "vgdata" using metadata type lvm2

# vgchange -a y

  1 logical volume(s) in volume group "vgdata" now active

# lvscan 

  ACTIVE            '/dev/vgdata/lvdata' [15,00 GiB] inherit

# mount /dev/vgdata/lvdata /mnt

DONE

Disable IPv6 when using apt-get

Sometimes when run command apt-get update, it connected to some repo using IPv6 address. But it made long delay because ISP's network was not ready for IPv6.
Config make use IPv4
- Add -o Acquire::ForceIPv4=true when run apt-get
- Make config persistent:

# echo 'Acquire::ForceIPv4 "true";' | tee /etc/apt/apt.conf.d/99force-ipv4 

Ubuntu cloud instance hang at boot screen

When you reboot ubuntu cloud instance, sometimes it hang in boot screen with some lines such as:
random: nonblocking pool is initialized
or
random: init urandom read with 94 bits of entropy available

Reboot it, hard reboot but it was still stuck at that.

Solution: migrate instance to another compute host

Kernel hanging tty in CentOS 6.6

In CentOS 6.6, version kernel 2.6.32-504.el6.x86_64, sometimes I could not connect to the server.
I can run ssh but can not get tty console.
After googling, I saw a question in stackoverflow
http://stackoverflow.com/questions/26628274/kernel-hanging-the-tty-subsystem
/var/log/messages

 kernel: INFO: task bash:44739 blocked for more than 120 seconds.
 kernel:      Not tainted 2.6.32-504.el6.x86_64 #1
 kernel: "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
 kernel: bash          D 0000000000000006     0 44739      1 0x00000080
 kernel: ffff88023acaf898 0000000000000046 0000000000000000 ffff8803b5580d00
 kernel: ffff88023acaf868 ffffffff81271aa4 00004e9cd768ce30 ffff88043c279800
 kernel: ffff88043c2799e0 0000000105231542 ffff88023bbe5098 ffff88023acaffd8
 kernel: Call Trace:
 kernel: [] ? blk_queue_bio+0x494/0x610
 kernel: [] schedule_timeout+0x215/0x2e0
 kernel: [] wait_for_common+0x123/0x180
 kernel: [] ? default_wake_function+0x0/0x20
 kernel: [] wait_for_completion+0x1d/0x20
 kernel: [] flush_cpu_workqueue+0x61/0x90
 kernel: [] ? wq_barrier_func+0x0/0x20
 kernel: [] flush_workqueue+0x54/0x80
 kernel: [] flush_scheduled_work+0x15/0x20
 kernel: [] tty_ldisc_release+0x3c/0x90
 kernel: [] tty_release_dev+0x40b/0x5e0
 kernel: [] ? __dec_zone_page_state+0x2e/0x30
 kernel: [] tty_release+0x1e/0x30
 kernel: [] __fput+0xf5/0x210
 kernel: [] fput+0x25/0x30
 kernel: [] filp_close+0x5d/0x90
 kernel: [] put_files_struct+0x7f/0xf0
 kernel: [] exit_files+0x53/0x70
 kernel: [] do_exit+0x18d/0x870
 kernel: [] ? __sigqueue_free+0x3d/0x50
 kernel: [] ? __dequeue_signal+0x102/0x200
 kernel: [] do_group_exit+0x58/0xd0
 kernel: [] get_signal_to_deliver+0x1f6/0x460
 kernel: [] do_signal+0x75/0x800
 kernel: [] ? __audit_syscall_exit+0x25e/0x290
 kernel: [] do_notify_resume+0x90/0xc0
 kernel: [] int_signal+0x12/0x17

or

 kernel: INFO: task sshd:25489 blocked for more than 120 seconds.
 kernel:      Not tainted 2.6.32-504.el6.x86_64 #1
 kernel: "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
 kernel: sshd          D 0000000000000000     0 25489  26121 0x00000080
 kernel: ffff88023a8cf728 0000000000000082 0000000000000000 0000000000000000
 kernel: ffff88023a8cf7f8 ffffffff8105ca34 00006b83e91acd8b ffff88023a8cf708
 kernel: ffff88023a8cf880 00000001070847e8 ffff880239e48638 ffff88023a8cffd8
 kernel: Call Trace:
 kernel: [] ? find_busiest_group+0x244/0x9e0
 kernel: [] schedule_timeout+0x215/0x2e0
 kernel: [] wait_for_common+0x123/0x180
 kernel: [] ? default_wake_function+0x0/0x20
 kernel: [] wait_for_completion+0x1d/0x20
 kernel: [] flush_work+0x77/0xc0
 kernel: [] ? wq_barrier_func+0x0/0x20
 kernel: [] flush_delayed_work+0x54/0x70
 kernel: [] tty_flush_to_ldisc+0x15/0x20
 kernel: [] n_tty_poll+0x67/0x1d0
 kernel: [] tty_poll+0x8a/0xa0
 kernel: [] do_select+0x3c5/0x7c0
 kernel: [] ? ip_finish_output+0x148/0x310
 kernel: [] ? __pollwait+0x0/0xf0
 kernel: [] ? pollwake+0x0/0x60
 kernel: [] ? pollwake+0x0/0x60
 kernel: [] ? pollwake+0x0/0x60
 kernel: [] ? pollwake+0x0/0x60
 kernel: [] ? _spin_unlock_bh+0x1b/0x20
 kernel: [] ? release_sock+0xe5/0x110
 kernel: [] ? tcp_sendmsg+0x73c/0xa20
 kernel: [] ? sock_aio_write+0x19b/0x1c0
 kernel: [] ? tty_wakeup+0x3d/0x80
 kernel: [] core_sys_select+0x18a/0x2c0
 kernel: [] ? n_tty_read+0x3ad/0x950
 kernel: [] ? autoremove_wake_function+0x0/0x40
 kernel: [] sys_select+0x47/0x110

Solution: yum upgrade to install new kernel, and reboot system to using new kernel.

Fix SSH long delay connection in CentOS

Add 2 options in /etc/ssh/sshd_config

UseDNS no
GSSAPIAuthentication no

Reload: systemctl reload sshd