| author | date | language | license | source |
|---|---|---|---|---|
Justin Ellingwood |
2016-07-13 |
en |
cc by-nc-sa |
There are many tools available to manage storage in Linux. However, only a handful are used for day-to-day maintenance and administration. In this guide, we will cover some of the most commonly used utilities for managing mount points, storage devices, and filesystems.
This guide will not cover how to prepare storage devices for their initial use on a Linux system. Our guide on partitioning and formatting block devices in Linux will help you prepare your raw storage device if you have not set up your storage yet.
For more information about some of the terminology used to discuss storage, take a look at our article on storage terminology.
Often, the most important information you will want to find out about the storage on your system is the capacity and current utilization of the connected storage devices.
To check how much storage space is available in total and to see the current utilization of your drives, use the df utility. By default, this outputs the measurements in 1K blocks, which isn’t usually too useful. Add the -h flag to output in human-readable units:
df -h
OutputFilesystem Size Used Avail Use% Mounted on
udev 238M 0 238M 0% /dev
tmpfs 49M 624K 49M 2% /run
/dev/vda1 20G 1.1G 18G 6% /
tmpfs 245M 0 245M 0% /dev/shm
tmpfs 5.0M 0 5.0M 0% /run/lock
tmpfs 245M 0 245M 0% /sys/fs/cgroup
tmpfs 49M 0 49M 0% /run/user/1000
/dev/sda1 99G 60M 94G 1% /mnt/data
As you can see, the /dev/vda1 partition, which is mounted at /, is 6% full and has 18G of available space, while the /dev/sda1 partition, which is mounted at /mnt/data is empty and has 94G of available space. The other entries use tmpfs or devtmpfs filesystems, which is volatile memory used as if it were permanent storage. We can exclude these entries by typing:
df -h -x tmpfs -x devtmpfs
OutputFilesystem Size Used Avail Use% Mounted on
/dev/vda1 20G 1.1G 18G 6% /
/dev/sda1 99G 60M 94G 1% /mnt/data
This output offers a more focused display of current disk utilization by removing some pseudo- and special devices.
A block device is a generic term for a storage device that reads or writes in blocks of a specific size. This term applies to almost every type of non-volatile storage, including hard disk drives (HDDs), solid state drives (SSDs), flash memory, etc. The block device is the physical device where the filesystem is written. The filesystem, in turn, dictates how data and files are stored.
The lsblk utility can be used to display information about block devices easily. The specific capabilities of the utility depend on the version installed, but in general, the lsblk command can be used to display information about the drive itself, as well as the partitioning information and the filesystem that has been written to it.
Without any arguments, lsblk will show device names, the major and minor numbers (used by the Linux kernel to keep track of drivers and devices), whether the drive is removable, its size, whether it is mounted read-only, its type (disk or partition), and its mount point. Some systems require sudo for this to display correctly, so we will use that below:
sudo lsblk
OutputNAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
sda 8:0 0 100G 0 disk
vda 253:0 0 20G 0 disk
└─vda1 253:1 0 20G 0 part /
Of the output displayed, the most important parts will usually be the name, which refers to the device name under /dev, the size, the type, and the mountpoint. Here, we can see that we have one disk (/dev/vda) with a single partition (/dev/vda1) being used as the / partition and another disk (/dev/sda) that has not been partitioned.
To get information more relevant to disk and partition management, you can pass the --fs flag on some versions:
sudo lsblk --fs
OutputNAME FSTYPE LABEL UUID MOUNTPOINT
sda
vda
└─vda1 ext4 DOROOT c154916c-06ea-4268-819d-c0e36750c1cd /
If the --fs flag is unavailable for your version, you can manually replicate the output by using the -o flag to request specific output. You can use -o NAME,FSTYPE,LABEL,UUID,MOUNTPOINT to get this same information.
To get information about the disk topology, type:
sudo lsblk -t
OutputNAME ALIGNMENT MIN-IO OPT-IO PHY-SEC LOG-SEC ROTA SCHED RQ-SIZE RA WSAME
sda 0 512 0 512 512 1 deadline 128 128 2G
vda 0 512 0 512 512 1 128 128 0B
└─vda1 0 512 0 512 512 1 128 128 0B
There are many other shortcuts available to display related traits about your disks and partitions. You can output all available columns with the -O flag or you can customize the fields to display by specifying the column names with the -o flag. The -h flag can be used to list the available columns:
lsblk -h
Output. . .
Available columns (for --output):
NAME device name
KNAME internal kernel device name
. . .
SUBSYSTEMS de-duplicated chain of subsystems
REV device revision
VENDOR device vendor
For more details see lsblk(8).
Before you can use a new disk, you typically have to partition it, format it with a filesystem, and then mount the drive or partitions. Partitioning and formatting are usually one time procedures, so we won’t discuss them here. As mentioned earlier, you can find out more information on how to partition and format a drive with Linux in this article.
Mounting, on the other hand, is something you may manage more frequently. Mounting the filesystem makes it available to the server at the selected mount point. A mount point is simply a directory under which the new filesystem can be accessed.
Two complementary commands are primarily used to manage mounting: mount and umount. The mount command is used to attach a filesystem to the current file tree. In a Linux system, a single unified file hierarchy is used for the entire system, regardless of how many physical devices it is composed of. The umount command (Note: this is umount, not unmount) is used to unmount a filesystem. Additionally, the findmnt command is helpful for gathering information about the current state of mounted filesystems.
The most basic way to use mount is to pass in a formatted device or partition and the mount point where it is to be attached:
sudo mount /dev/sda1 /mnt
The mount point, the final parameter which specifies where in the file hierarchy the new filesystem should be attached, should almost always be an empty directory.
Usually, you will want to select more specific options when mounting. Although mount can attempt to guess the filesystem type, it’s almost always a better idea to pass in the filesystem type with the -t option. For an Ext4 filesystem, this would be:
sudo mount -t ext4 /dev/sda1 /mnt
There are many other options that will impact the way that the filesystem is mounted. There are generic mount options, which can be found in the FILESYSTEM INDEPENDENT MOUNT OPTIONS section of man mount. Filesystems also typically have a section under the FILESYSTEM SPECIFIC MOUNT OPTIONS header in the same man page filesystem-dependent options.
Pass in other options with the -o flag. For instance, to mount a partition with the default options (which stands for rw,suid,dev,exec,auto,nouser,async), we can pass in -o defaults. If we want to override the read-write permissions and mount as read-only, we can add ro as a later option, which will override the rw from the defaults option:
sudo mount -t ext4 -o defaults,ro /dev/sda1 /mnt
To mount all of the filesystems outlined in the /etc/fstab file, you can pass the -a option:
sudo mount -a
To display the mount options used for a specific mount, pass it to the findmnt command. For instance, if we viewed the read-only mount that we gave as an example above with findmnt, it would look something like this:
findmnt /mnt
OutputTARGET SOURCE FSTYPE OPTIONS
/mnt /dev/sda1 ext4 ro,relatime,data=ordered
This can be incredibly useful if you have been experimenting with multiple options and have finally discovered a set that you like. You can find the options it is using with findmnt so that you know what is appropriate to add to the /etc/fstab file for future mounting.
The umount command is used to unmount a given filesystem. Again, this is umount not unmount.
The general form of the command is simply to name the mount point or device of a currently mounted filesystem. Make sure that you are not using any files on the mount point and that you do not have any applications (including your current shell) operating inside of the mount point:
cd ~
sudo umount /mnt
For the vast majority of users, nothing beyond the default unmounting behavior will ever be necessary.
While this list is in no way exhaustive, these utilities should cover most of what you need for daily system administration tasks. By learning a few tools, you can easily handle storage devices on your server.