CST8177 Ð Linux II
Disks, Filesystems, Booting 
Todd Kelley 
kelleyt@algonquincollege.com 

CST8177Ð Todd Kelley 
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.sudo and PATH (environment) 

.disks 

.partitioning 

.formatting file systems: mkfs command 

.checking file system integrity: fsck command 

./etc/fstab 

.mounting file systems: mount command 

.unmounting file systems: umount command 

.lsof and fuser      


 
     

2 
TodayÕs Topics





.builtin command (part of the shell itself, so there's no notion of "where" the command is) 

.echo "Hello world" 

.exit 2        # inside a script, for example  


.by absolute pathname (does not depend on PATH variable): 

./bin/ls -l 

./usr/sbin/useradd newuser 

./usr/bin/sudo Ði 

."$HOME"/bin/myscript.sh   # shell expands $HOME so this is really /home/username/bin/myscript.sh 




Executing a command (review)
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.by relative pathname (does not depend on PATH variable, but DOES depend on your current directory Ð interactive shells only) 

.You MUST NOT do any of these in a shell script 

../myscript.sh    # script is in current directory 

.../myprogram   # script is in parent directory 

.../../somedir/anotherscript.sh # two dirs up, then one directory down 

.bin/mycommand  # assumes "bin" is a directory in the current directory   




Executing a command (cont'd)
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.using the PATH environment variable 

.ls -l 

.cp foo ../bar 

.rm ../bar/foo 


.none of these commands will run unless they reside in a directory that is listed in the PATH environment variable 

.Now that we are using root privileges, we need to be aware that root has a different PATH than your non-root user 



Executing a command (cont'd)
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.sudo command # just run the command 

.you get 5 min by default to invoke sudo again without password 

.example$ sudo head /etc/shadow 


.sudo Ðs   # superuser shell with current env 

.sudo Ði   # simulate root login (root's env) 

.sudo Ðs leaves you in the same directory, and with the same PATH 

.to take on root's environment including PATH: 

.sudo Ði 

.or 

.sudo Ðs followed by su - 




sudo and your environment
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.partitioning 

.LVM 

.formatting file systems 

.mounting file systems 

./etc/fstab 



Disks and disk management
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.A partition is a section of disk forming a physical volume that contain a files ystem, or swap space, or be used as a component in LVM or RAID  

.The Master Boot Record contains the Disk Partition Table, which can hold up to four entries due to the way in which the master boot record is structured 

.With certain specialty tools, you can create more than four partitions, but we'll stick to the MSDOS partition table format  


.Each Disk Partition Table entry describes a partition by specifying its:  

.first cylinder 

.last cylinder 

.whether it is bootable 

.a partition type identifier. 




CST8207 - Algonquin College 
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Overview of partitioning (8207 review)





.We deal primarily with the MSDOS Partition Table type 

.GPT partition tables getting common: GUID Partition Table 

.Globally Unique IDentifier  (but back to MSDOS TablesÉ) 


 
.Up to four Primary Partitions are possible in a single table  

.At most one of the four Primary partitions can be an Extended Partition  

.Logical Partitions can be created inside an Extended Partition  



CST8177 - Algonquin College 
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Partitioning





CST8177 - Algonquin College 
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Identifying Partitions
Lin_DPT
Naming partitions .sdx1 Ð sdx4 

¥Primary Partitions recorded in the partition table 


.sdx5 Ð sdx63 

¥Logical partitions 




Note: You can have up to 4 primary partitions created in your            system, while there can be only one extended partition.  
Sda1 
Sda2 

Sda3 
Sda5 
Sda6 
Sda7 





fdiskfdisk.Disk Druid  .gparted.DOS fdisk program 

.Very limited Linux support 


.Linux fdisk program (we use this) 

.similar to DOS fdisk, but more features available 

.can only be used under Linux/UNIX 


.parted can handle more partition table types (e.g. GPT)  

.Disk Druid program 

.Part of the Fedora installation system 

.Cannot be run on its own 


.gparted (Fedora, Ubuntu) 

.Gnome Partitioning Editor: GUI based partitioning 

.only runs from within Linux/UNIX   




CST8177 - Algonquin College 
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Options for Partitioning





.fdisk [options] device .fdisk [options] device 

.command-line partition table manipulator for Linux 

.allows for viewing or modifying existing partition table and/or creating new partition(s) for a specified device 

.can set Partition Type for most of the common files systems in use today 

.fdisk Ðl /dev/sda  




CST8177 - Algonquin College 
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Linux fdisk command





Our Partition Table
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Screen Shot 2013-03-11 at 7.20.16 AM.png





LVM
.Logical Volume Manager 

.LVM tutorial:  

.http://www.howtoforge.com/linux_lvm 


.disk partitions are physical volumes 

.one or more physical volumes forms a volume group 

.a volume group can be divided into logical volumes 

.We create file systems on the logical volumes 








LVM Logical Volume Components






SoÉ What happened when we installed CentOS?
.By default, LVM was used to set up the /dev/sda2 partition. 

.Disk Druid set up /dev/sda1 and /dev/sda2 

./dev/sda1 was set as bootable and contains  


 /boot (no LVM involved with /dev/sda1) 
.To actually see where things are you can do the following: 

.mount 

.lvdisplay  # show logical volumes 

.pvdisplay  # show physical volumes 









./dev/sda divided into 2 partitions: 

./dev/sda1 : boot partition (no LVM) 

./dev/sda2 : physical volume for LVM 


./dev/sda2 is the only physical volume in VolGroup00 


 

Our CentOS LVM setup
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Screen Shot 2013-03-11 at 7.37.53 AM.png





.VolGroup00 is divided into 2 logical volumes 

.LogVol00 is root filesystem, LogVol01 is swap  



Logical Volumes
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Screen Shot 2013-03-11 at 7.40.08 AM.png





.We could do by hand what the Red Hat installer did: 

.pvcreate /dev/sda2     # initialize /dev/sda2 as physical volume for LVM 

.vgcreate VolGroup00 /dev/sda2   #create volume group (a group of 1: /dev/sda2 is the only physical volume in group) 

.lvcreate --name LogVol00 --size 1.34G VolGroup00 

.create a logical volume LogVol00  in volume group VolGroup00 


.lvcreate --name LogVol01 --size 352M VolGroup00 

.create a second logical volume LogVol01 in volume group VolGroup00 


.mkfs Ðt ext3 /dev/VolGroup00/LogVol00 

.make a file system in logical volume LogVol00 


.mkswap /dev/VolGroup00/LogVol01 

.swapon /dev/VolGroup00/LogVol01 

.use the other logical volume LogVol01 for swap space  




LVM commands
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.http://teaching.idallen.com/cst8207/13w/notes/720_partitions_and_file_systems.html 



File systems (8207 review)
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.no drive letters! 



Linux/Unix mounting
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                          / var/                           tmp/                      home/    file1                          afile                        dir1/    file2                          bfile                            file1                                                                       file 2 
/dev/sda2 
              / tgk/                           idallen/                      donellr/    file1                          afile                             file2     file                            file 
/dev/sda3 





.mount /dev/sda3 /home 



Linux/Unix mounting
CST8177 Ð Todd Kelley 
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                          / var/                           tmp/                      home/    file1                          afile                        dir1/    file2                          bfile                            file1                                                                       file 2 
/dev/sda2 
       home/ tgk/                           idallen/                      donellr/    file1                          afile                             file2    file                            file 
/dev/sda3 



.the /home directory name still on /dev/sda2 

.the contents of /home are on /dev/sda3 

.the previous contents of /home are hidden 








.touch /home/donellr/file3 



Linux/Unix mounting
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                          / var/                           tmp/                      home/    file1                          afile                        dir1/    file2                          bfile                            file1                                                                       file 2 
/dev/sda2 
       home/ tgk/                           idallen/                      donellr/    file1                          afile                             file2    file                            file                               file3 
/dev/sda3 








.umount /dev/sda3 



Linux/Unix mounting
CST8177 Ð Todd Kelley 

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                          / var/                           tmp/                      home/    file1                          afile                        dir1/    file2                          bfile                            file1                                                                       file 2 
/dev/sda2 
              / tgk/                           idallen/                      donellr/    file1                          afile                             file2       file                            file                             file3 
/dev/sda3 





.man 5 fstab 

.note that records for swap space appear in /etc/fstab, although swap space is not a filesystem (files are not stored in swap space) 

.first field: device name 

.second field: mount point 

.third field: type 

.fourth field: mount options 

.fifth field: backup related (dump program) 

.sixth field: file system check order  



/etc/fstab
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.mount options 

.on CentOS 5.8, "defaults" means 

.rw: read and write 

.dev: interpret device nodes 

.suid: setuid and setgid bits take effect 

.exec: permit execution of binaries 

.auto: mount automatically due to "mount -a" 

.nouser: regular users cannot mount  

.async: file I/O done asynchronously 


.other options: 

.these are for quota utilities to see rather than mount 

.usrquota 

.grpquota 






/etc/fstab (cont'd)
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.http://teaching.idallen.com/cst8207/13w/notes/580_system_log_files.html 

.kernel messages are kept in a ring buffer 

.common way to access the boot messages, including device discovery 

.dmesg 

.example: look for disk discovery: 

.dmesg | grep sd 


.(another way): look at disks/partitions that the kernel knows about: 

.cat /proc/partitions 




dmesg: kernel ring buffer
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.# migrating the /usr directory to be a separate partition on new disk 

.shut down machine 

.connect new disk to machine 

.power on machine 

.partition new disk (fdisk command) 

.make filesystem in new partition (mkfs command) 

.single user mode (shutdown command) 

.ensure target directory is backed up 

.move the target directory out of way (/usr to /usr1) (mv command) 

.create the mount point (to replace dir we just moved, same name) 

.mount new filesystem (mount command) 

./usr1/bin/rsync ÐaHv /usr1/. /usr    (notice where rsync is!) 

.add a record for the new filesystem /etc/fstab 

.exit, to return to runlevel 3 

.remove /usr1 (content should be backed up)  



Adding a disk
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.when trying to unmount a filesystem, you might get an error: 


umount: /dirname: device is busy 
.probably some process is using the filesystem (it's busy -- make sure you're not in that directory!) 

.lsof /mountpoint  # list open files in the filesystem mounted on /mountpoint 


lsof +D /directory 
this will show you what processes are using the directory or (+D) any directory under it 

device busy
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.Note the difference between a mountpoint and a directory 

.mountpoint: both of these commands will apply to the entire filesystem mounted there 

.directory: both of these commands will apply to just that directory, not recursively every subdirectory underneath it  


.summary of lsof: 

.http://www.thegeekstuff.com/2012/08/lsof-command-examples/ 



 
.fuser: similar in purpose to lsof 

.examples: 

.fuser /mountpoint   # all processes using the filesystem mounted at /mountpoint 

.fuser /home/dir      # all processes using the directory dir 


.summary of fuser: 

.http://www.thegeekstuff.com/2012/02/linux-fuser-command/  



 

lsof and fuser
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.http://teaching.idallen.com/cst8207/13w/notes/750_booting_and_grub.html 

.page numbers for Fifth Edition Sobell: 

.Chapter 11: 424-431 

.Chapter 15: 551-552 




Booting
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