EXAM OBJECTIVES COVERED
1.4 Given a scenario, manage storage in a Linux environment.
2.7 Explain the use and operation of Linux devices.
4.1 Given a scenario, analyze system properties and remediate accordingly.
The /proc/mounts File
To display all mounted file systems Linux provides the information in /proc/mounts. It is actually not a real file, but part of the virtual file system that represents the status of mounted objects as reported by the Linux kernel. It is in a format similar to the /etc/fstab file: the mounted device, the mount point, the file system type, mount flags, dump frequency, and file system check order. Even though it is not truly a file, you can use commands like cat or less on this "file."
The /etc/mtab File
This file lists all currently mounted filesystems along with their initialization options. mtab is very similar to /proc/mounts in that they both report the status of currently mounted file systems. However, since the kernel updates /proc/mounts is typically more accurate and includes more up-to-date information about the file systems. The mount command maintains the contents of the mtab file.
The /proc/partitions File
The /proc/partitions file contains partition block allocation information. Like the other files in the /proc file system, it is not a real file but part of the virtual file system. The format of /proc/partitions contains 4 columns:
• major—This value represents the class of device so that it can be mapped to an appropriate driver.
• minor—This value separates partitions into physical devices. This corresponds to the number at the end of the partition's name (such as sda1, sda2, etc).
• #blocks—How many physical blocks the partition takes up.
• name—The name of the partition.
major minor #blocks name 8 0 488386584 sda 8 1 9216000 sda1 8 2 81920000 sda2 8 5 81920000 sda5 8 6 315317248 sda6 8 7 8192 sda7 11 0 1048575 sr0
The lsblk Command
The lsblk command lists information about all available or the specified block devices. The lsblk command reads the sysfs filesystem and udev db to gather information. If the udev db is not available or lsblk is compiled without udev support than it tries to read LABELs, UUIDs and filesystem types from the block device. In this case root permissions are necessary.
lsblk [ OPTIONS ] lsblk [ OPTIONS ] device
|-a, --all||Also list empty devices. (By default they are skipped.)|
|-e, --exclude list||Exclude the devices specified by the comma-separated list of major device numbers. Note that RAM disks (major=1) are excluded by default. The filter is applied to the top-level devices only.|
|-f, --fs||Output info about filesystems. This option is equivalent to -o NAME,FSTYPE,LABEL,UUID,MOUNTPOINT. The authoritative information about filesystems and raids is provided by the blkid(8) command.|
|-l, --list||Produce output in the form of a list.|
|-m, --perms||Output info about device owner, group and mode. This option is equivalent to -o NAME,SIZE,OWNER,GROUP,MODE.|
|-n, --noheadings||Do not print a header line.|
|-o, --output list||Specify which output columns to print. Use --help to get a list of all supported columns.
The default list of columns may be extended if list is specified in the format +list (e.g. lsblk -o +UUID)./pre>
A simple example:
pbmac@pbmac-server $ lsblk -f NAME FSTYPE LABEL UUID MOUNTPOINT loop0 squashf /snap/core18/1705 loop1 squashf /snap/core18/1754 loop2 squashf /snap/nmap/1356 sda ├─sda1 ext4 / 6e73a278-7609-4612-b1dc-5e7451bb3f0d / ├─sda2 ext4 /usr 815e345f-4e06-4a42-b19d-35cf6ef7fd32 /usr ├─sda5 ext4 /var ad74f5a8-188a-4282-93a4-2107dfb08fc5 /var ├─sda6 ext4 /home 3709f1b7-6417-413e-a4cd-2bec3002ba25 /home └─sda7 swap 68e33827-8998-49f9-98a1-94415abad3bb [SWAP]
The blkid Command
The blkid command reads information directly from devices and for non-root users it returns cached unverified information. blkid is mostly designed for system services and to test libblkid functionality. Options and syntax are very similar to the lsblk command.
blkid [options] [device name]
When device is specified, tokens from only this device are displayed. It is possible to specify multiple device arguments on the command line. If none is given, all devices which appear in /proc/partitions are shown, if they are recognized. See the blkid man page for additional options.
pbmac@pbmac-server $ blkid /dev/sda1: LABEL="/" UUID="6e73a278-7609-4612-b1dc-5e7451bb3f0d" TYPE="ext4" PARTUUID="a3f88df0-01" /dev/sda2: LABEL="/usr" UUID="815e345f-4e06-4a42-b19d-35cf6ef7fd32" TYPE="ext4" PARTUUID="a3f88df0-02" /dev/sda5: LABEL="/var" UUID="ad74f5a8-188a-4282-93a4-2107dfb08fc5" TYPE="ext4" PARTUUID="a3f88df0-05" /dev/sda6: LABEL="/home" UUID="3709f1b7-6417-413e-a4cd-2bec3002ba25" TYPE="ext4" PARTUUID="a3f88df0-06" /dev/sda7: UUID="68e33827-8998-49f9-98a1-94415abad3bb" TYPE="swap" PARTUUID="a3f88df0-07" pbmac@pbmac-server $ blkid -i sda1 /dev/sda1: MINIMUM_IO_SIZE="512" PHYSICAL_SECTOR_SIZE="512" LOGICAL_SECTOR_SIZE="512"