CST8177 Đ Linux II Disks, File systems, Booting Todd Kelley kelleyt@algonquincollege.com CST8177Đ Todd Kelley 1 .bind mounts .quotas .Installation Disk rescue mode .more booting 2 TodayƠs Topics .A bind mount is used to mount a directory onto a mount point: man mount .use the ̉bindÓ option for the mount command # mount Đo bind /some/dir /anotherdir .now /some/dir and /anotherdir are the same directory .Be careful with bind mounts, because they make it possible to form cycles in the file system .e.g. dangerous: "mount Đo bind /home /home/user/dir" .serious repercussions for .rm Đrf /home/user # will remove all of /home .find /home/user # will never stop .any program that recursively descends directories Bind mounts CST8177 Đ Todd Kelley 3 .make an inaccessible directory accessible: .mount Đo bind /home/user/private/public /public .make disk space in one file system available in another file system .suppose you have a large separate file system with lots of free space on /var, and root file system with /home is nearly full: .mkdir /var/local/home/{user1,user2} .move contents of /home/{user1,user2,...} to /var/local/home .mount Đo bind /var/local/home /home .beware: new /home has same mount options as /var Bind mount examples CST8177 Đ Todd Kelley 4 .share directories across chroot environments .mount Đo bind /dev /home/user/myroot/dev .chroot /home/user/myroot/dev .in the chroot-ed environment, /dev will be the same as the un-chroot-ed /dev Bind mount examples (cont'd) CST8177 Đ Todd Kelley 5 .https://access.redhat.com/knowledge/docs/en-US/Red_Hat_Enterprise_Linux/6/html/Storage_Administration_Guide/ch-disk-quotas.html .Example: enabling quotas on /home ./etc/fstab: usrquota,grpquota mount options for file system containing /home .quotacheck Đcug /home .c: don't read quota files, create new quota files .u: do user quotas .g: do group quotas .edquota username or setquota -u user soft hard isoft ihard fs .edquota Đt # edit grace period .quotaon Đvaug # turn quotas on .repquota Đa # report on quotas .quotaoff Đvaug; quotacheck Đvaug; quotaon Đvaug #single user mode Quotas CST8177 Đ Todd Kelley 6 .There are dangers associated with doing file system operations on "system directories" that might be used in system operation. .For example, many programs will use the shared libraries in /usr/lib, which disappear if we move /usr .Also, there may come a time when the system won't boot properly: MBR corrupted, bad entry in /etc/fstab, inconsistent / file system Installation DVD for rescue mode / Live CD CST8177 Đ Todd Kelley 7 .To boot into rescue mode .ensure BIOS boot order is set for booting from CD/DVD before Hard Drive (even in VMware Đ F2 to enter setup) .insert the installation DVD into drive (or the iso image into the virtual DVD drive) .boot the system .type "linux rescue" at the prompt .Linux will run "from" the DVD (Live CD), not from your file systems (your system is not running) .It will offer to search for and mount your Linux file systems on /mnt/sysimage linux rescue CST8177 Đ Todd Kelley 8 .The Live CD Linux system can see your hard drives, and this is how you can repair or alter what is on those hard drives .You need to remember that a Live CD Linux system is running from its own root filesystem (like dual boot?), so this means .the users are different /etc/passwd /etc/shadow, etc (or should I say all of /etc) are different .the services running, firewalling, and so on, are different linux rescue (cont'd) CST8177 Đ Todd Kelley 9 Rescue mode / Live CD CST8177 Đ Todd Kelley 10 / etc/ bin/ dev/ passwd ls sda shadow bash VolGroup00/ LogVol00 ramdisk / etc/ home/ dev/ fstab idallen/ VolGroup00/ passwd donnelr LogVol00 /dev/VolGroup00/LogVol00 .Fix /etc/fstab .mount /dev/VolGroup00/LogVol00 /mnt/sysimage (if it isn't already mounted) .vi /mnt/sysimage/etc/fstab .fix the problem .save and quit .exit linux rescue example 1 CST8177 Đ Todd Kelley 11 .fix MBR .# our root file system is mounted on /mnt/sysimage .chroot /mnt/sysimage .# now / is our root file system! .# our boot filesystem is mounted on /boot .grub-install /dev/sda .Whoa! That chroot thing was neat .chroot runs a program or interactive shell using the named directory as the root directory .Default program is ${SHELL} Đi .This simulates running off our system's root file system without going through its boot process linux rescue example 2 CST8177 Đ Todd Kelley 12 .That LVM tutorial link again: .http://www.howtoforge.com/linux_lvm .Because Red Hat's installer used Disk Druid to set up LVM and installed the root file system on a Logical Volume, we can .add a hard disk .create a partition on that hard disk .# or, maybe we already had an unused partition, such as a reclaimed Windows partition .set up that partition as a physical volume .add that physical volume to our Volume Group .grow the Logical Volume on the Volume Group .grow the file system on that Logical Volume Growing a filesystem CST8177 Đ Todd Kelley 13 .set up our "new" or "spare" partition as a physical volume for LVM: .pvcreate /dev/sdb1 .Add this new physical volume to a volume group (in this case VolGroup00): .vgextend VolGroup00 /dev/sdb1 .See how many free extents (Free PE) are available in this volume group (VolGroup00) .vgdisplay Growing a file system (cont'd) CST8177 Đ Todd Kelley 14 .Suppose the previous "vgdisplay" command showed that VolGroup00 had 319 free extents ("Free PE") and we use them all: .lvextend Đl+319 /dev/VolGroup00/LogVol00 .Now LogVol00, which contains our root file system, is bigger, but the filesystem is still the same size. .Grow the filesystem (ext3) to fill the added space: .resize2fs /dev/VolGroup00/LogVol00 .Use df command so see we have bigger root file system now! Growing a file system (cont'd) CST8177 Đ Todd Kelley 15 .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 CST8177 Đ Todd Kelley 16 .Power button pressed .BIOS .POST .MBR : contains grub stage 1 .grub stage 1 : to find grub stage 2 .grub stage 2 : to launch kernel .kernel running .init process (PID 1) : consults inittab ./etc/inittab ./etc/init.d/rc.sysinit ./etc/rc.d/rc 3 : assuming default runlevel 3 Booting Sequence (CentOS) CST8177 Đ Todd Kelley 17 ./etc/init.d/* .these are scripts for starting, stopping, restarting services ./etc/rc.d/rc.N.d/* #where N is a runlevel .these are symbolic links to service's script .begins with K means service should not be running in that runlevel: call it with "stop" argument .begins with S means service should be running in that runlevel: call it with "start" argument .chkconfig maintains these scripts SysVinit CST8177 Đ Todd Kelley 18