CST8177 – Linux II Disks, Filesystems 1 .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 Today’s 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 –i ."$HOME"/bin/myscript.sh # shell expands $HOME so this is really /home/username/bin/myscript.sh Executing a command (review) 3 .by relative pathname (does not depend on PATH variable, but DOES depend on your current directory – interactive shells only) .You MUST NOT do any of these in a shell script ../myscript.sh # script is in current directory .../myprogram # script is in parent directory .../../somedir/anotherscript.sh # two dirs up, then one directory down .bin/mycommand # assumes "bin" is a directory in the current directory Executing a command (cont'd) 4 .using the PATH environment variable .ls -l .cp foo ../bar .rm ../bar/foo .none of these commands will run unless they reside in a directory that is listed in the PATH environment variable .Now that we are using root privileges, we need to be aware that root can have a different PATH than your non-root user Executing a command (cont'd) 5 .sudo command # just run the command .you get 5 min by default to invoke sudo again without password .example$ sudo head /etc/shadow .sudo –s # superuser shell with current env .sudo –i # simulate root login (root's env) .sudo –s leaves you in the same directory, and with the same PATH .to take on root's environment including PATH: .sudo –i .or .sudo –s followed by su - sudo and your environment 6 .partitioning .formatting file systems .mounting file systems ./etc/fstab Disks and disk management 7 .A partition is a section of disk forming a physical volume that contain a filesystem, 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. 8 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 Tables…) .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 9 Partitioning 10 Identifying Partitions Lin_DPT Naming partitions .sdx1 – sdx4 •Primary Partitions recorded in the partition table .sdx5 – 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 11 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 –l /dev/sda 12 Linux fdisk command .power down machine (or virtual machine) .add hard disk .power up machine .verify the new disk was detected (following slide) .if the disk was brand new, it won't be partitioned (our example is this case) .if the disk is being reused, be sure you can identify its partitions and you do not need the data Add a disk 13 .http://teaching.idallen.com/cst8207/14w/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 14 dmesg 15 /proc/partitions 16 .use fdisk to partition the new disk Create partition on new disk 17 .http://teaching.idallen.com/cst8207/14w/notes/720_partitions_and_file_systems.html File systems (8207 review) 18 Linux/Unix mounting 19 / var/ tmp/ home/ file1 afile dir1/ file2 bfile file1 file 2 /dev/sda2 / wjiang/ idallen/ donellr/ file1 afile file2 file file /dev/sda3 .mount /dev/sda3 /home Linux/Unix mounting 20 / var/ tmp/ home/ file1 afile dir1/ file2 bfile file1 file 2 /dev/sda2 home/ wjiang/ 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 21 / var/ tmp/ home/ file1 afile dir1/ file2 bfile file1 file 2 /dev/sda2 home/ wjiang/ idallen/ donellr/ file1 afile file2 file file file3 /dev/sda3 .umount /dev/sda3 Linux/Unix mounting 22 / var/ tmp/ home/ file1 afile dir1/ file2 bfile file1 file 2 /dev/sda2 / wjiang/ idallen/ donellr/ file1 afile file2 file file file3 /dev/sda3 .fsck, mount, and umount use this file .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 23 .mount –a .issued as part of the boot process .all file systems listed in /etc/fstab will be mounted accordingly (except those with "noauto" option or "ignore" file system type) .mount .mount will consult /etc/fstab to find the device and options for that mount point, and mount it .mount .mount will consult /etc/fstab to find the mount point and options for that mount point, and mount it /etc/fstab commands 24 .device name, the first field, names the block special device (e.g. /dev/sda1) on which the file system resides .the first field can also be expressed in terms of LABEL or UUID (e.g. LABEL=root) (e.g. see the /etc/fstab on our CentOS 6.5 machines) .blkid command prints the UUIDs of the system's block devices .e2label command prints/sets file system labels /etc/fstab: device name 25 .The mount point is the directory on which the file system should be mounted .swap is not a file system but is still controlled by /etc/fstab, so the mount point is none /etc/fstab: mount point 26 .ext4 is the file system type we use often ./proc/filesystems contains the list of file systems supported by the currently running kernel .swap for swap space .ignore for an unused filesystem .none for bind mounts /etc/fstab: file system type 27 .fourth field in /etc/fstab .expressed as a comma-separated list .different file systems support different options (see man 8 mount) .defaults: a set of default options .example options common to all file system types: .noauto: do not mount when "mount –a" called .user: allow a user to mount .owner: allow device owner to mount /etc/fstab: mount options 28 .mount options .on CentOS 6.5, "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 .relatime: update access times a certain way .other options: .these are for quota utilities to see rather than mount .usrquota .grpquota /etc/fstab: options (cont'd) 29 .the dump program uses this field to determine which file systems should be backed up by the dump command .the dump program can back up an entire file system to tape, for example .dump supports incremental backups .when restoring, it can provide an index of what's in the file system, do partial restores, etc .we don't use dump in this course /etc/fstab: dump 30 .the sixth and last field is used to determine the order in which file system checks are done at boot .root file system: 1 .other file systems: 2 .no fsck: 0 /etc/fstab: fsck order 31 ./etc/mtab is used by mount and umount to keep track of what is currently mounted .mount command (no args) prints this file ./proc/mounts is the kernel's list of what's mounted, and might be more up-to-date than /etc/mtab /etc/mtab and /proc/mounts 32 .# 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 –aHv /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 33 .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 34 .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 35