This is the unformatted notes....
Finishing off last week
A little exercise with initrd
cd /var/tmp
mkdir initrd
cd initrd
gunzip < /boot/initrd.img-3.13.0-100-generic | cpio -id
du -s *
Take a look at
bin directory
what is busybox?
init shellscript
it will call /bin/run-init to run /sbin/init
It is process #1
https://en.wikipedia.org/wiki/Init
https://en.wikipedia.org/wiki/Systemd
https://www.digitalocean.com/community/tutorials/understanding-systemd-units-and-unit-files
systemd is the future — (it spite of the screaming)
Fedora (2011), Red Hat (2014), Debian/Ubuntu/Raspbian (2015)
Still many System V compatiability modes
Connect to eastatoe.cs.unca.edu and look at /lib/systemd/services
Devices – Chapter 3
mknod
/proc/devices
https://github.com/torvalds/linux/tree/master/drivers
https://github.com/torvalds/linux/blob/master/drivers/char/mem.c
Look for read_null and write_null and null_lseek and null_fops
similarly for zero_fops and full_fops
and memdev structure (l 806)
https://github.com/torvalds/linux/blob/master/drivers/char/random.c
cat /dev/zero
echo foo > /dev/zero
echo foo > /dev/null
cat /dev/null
dd if=/dev/zero of=zero.chars bs=1000 count=1
ls -l /dev | grep " 1,"
/proc/filesystems
https://github.com/torvalds/linux/tree/master/fs/sysfs
/sys — sysfs
/proc — procfs
debugfs — /sys/kernel/debug
devpts — /dev/pts
Take a look at /sys — the sys filesystem
In /sys/bus
WHAT ARE THEY....
acpi
i2c
What is /sys/fs
cgroup, ecryptfs, ext4, fuse, pstore
What is /sys/module
What is a block vs character device?
block devices may "cache" blocks in RAM
take a look at the "top" command
What is a bus?
What are all the buses (in /sys/bus)
Look at Section 3.4
What are the disks on your system
Try
lsscsi
https://en.wikipedia.org/wiki/SCSI_command
http://www.seagate.com/staticfiles/support/disc/manuals/Interface%20manuals/100293068c.pdf
SCSI addresses by LBA not CHS
https://en.wikipedia.org/wiki/Cylinder-head-sector
What does this mean?
/sys/devices/pci0000:00/0000:00:1d.7/usb2/2-2/2-2:1.0/host12/target12:0:0/12:0:0:0/block/sdc
What is the northbridge and southbridge
Intel 4 Series Chipset
http://www.intel.com/content/www/us/en/processors/xeon/4-chipset-family-datasheet.html
Intel Z270 chipset
http://ark.intel.com/products/98089/
http://www.intel.com/content/www/us/en/chipsets/200-series-chipset-pch-datasheet-vol-1.html
Back to USB — what does the name mean?
http://www.makelinux.net/ldd3/chp-13-sect-2
mknod create devices
What can't ordinary users create devices?
Why aren't devices allowed on USB drives?
Section 3.5 — by the book
In the old days, you didn't add devices to running systems
lsusb
What is that device? (vendor + class)
https://usb-ids.gowdy.us
udev — dynamic device management
man udev
/etc/udev/rules.d/
udevadm — may need a USB device
udevadm info —query=all —name=/dev/sda
udevadm monitor
Look at udev-out.txt
Look at Figure 3-2
Disks, partitions, and file systems — Chapter 4
Why partitions?
http://www.digitalcitizen.life/4-reasons-why-you-should-use-more-one-partition-your-pc
The MBR (Master Book Record) world
Primary partitions — up to 4
Extended partition — 1 special primary partition
Logical partitions — a division of an extended partition
The GPT (Globally unique identifier Partition Table)
Other stuff —-
lvm — logical volume manager (look at the lab computer)
https://en.wikipedia.org/wiki/Logical_Volume_Manager_(Linux)
hardware RAID — on the server computers
software RAID
ZFS and AdvFS (defunct)
https://en.wikipedia.org/wiki/ZFS
https://en.wikipedia.org/wiki/AdvFS
Try out the Raspberry Pi
sudo /sbin/fdisk /dev/mmcblk0
Do not WRITE!
A partition exercise — Two year’s ago
DANGER. DANGER.
YOU MUST WATCH ME...