Both wget and curl are command line tools for transferring files over the network via various network protocols like HTTP or FTP. Wget is a GNU Project by the Free Software Foundation licensed under the GNU GPL whereas Curl is an independent project licensed under a variant of the MIT license.

Curl is also based on a libcurl library, part of the same project, which makes it more suitable for use in programming various applications. It is generally more flexible and featureful whereas wget is simpler.

Simple download

Here’s how to initiate a simple download with both wget and curl.

wget ftp://mirrors.kernel.org/gnu/unifont/unifont-7.0.01/unifont_upper-7.0.01.ttf

curl -O ftp://mirrors.kernel.org/gnu/unifont/unifont-7.0.01/unifont_upper-7.0.01.ttf

This will download the file to the current working directory with its original file name (which is what the -O option passed to curl is for). You can run curl without any options as well, but it will dump the file contents on to the screen as it downloads.

Download multiple files at once

You can also download multiple files in one go by specifying multiple URLs:

wget ftp://mirrors.kernel.org/gnu/unifont/unifont-7.0.01/unifont-7.0.01.ttf ftp://mirrors.kernel.org/gnu/unifont/unifont-7.0.01/unifont_upper-7.0.01.ttf

curl -O ftp://mirrors.kernel.org/gnu/unifont/unifont-7.0.01/unifont-7.0.01.ttf -O ftp://mirrors.kernel.org/gnu/unifont/unifont-7.0.01/unifont_upper-7.0.01.ttf

Specifying -O before each URL isn’t necessary, but we found that not specifying it results in the second file being downloaded being dumped into the command line.

That said, it is also possible to specify multiple files for download in accordance to a given range of numbers or letters in the file name.

With curl you can also download multiple files with sequential numbers or letters in their names like file1, file2, file3, and so on by specifying the range in the brackets:

curl -O ftp://example.com/file[1-50].txt

Multiple nested sequences are possible too, like this:

curl -O http://example.com/[2002-2014]/file{a-z}.txt

Resume downloads

Both wget and curl allow you to resume partial downloads, which is useful if a network outage in the middle of the download interrupted it, for example, and you want to continue where you left off.

With wget you simply use the -c or –continue option. Some have a habit of always passing this option just in case.

wget -c ftp://mirrors.kernel.org/gnu/unifont/unifont-7.0.01/unifont-7.0.01.ttf

With curl you can use the -C – options:

curl -C - ftp://mirrors.kernel.org/gnu/unifont/unifont-7.0.01/unifont-7.0.01.ttf

That’s in a nutshell how to use wget and curl. They’re both powerful, curl a bit more powerful than wget, and you can find all about what they can do in their manual pages: man wget, and man curl.

Every process in UNIX runs with a particular priority assigned to it, which determines how much processing time should it be allowed to use. Priorities are represented as numbers from -20 to 19 where -20 represents the highest priority, because -20 comes before every other number on that scale, and 19 is actually the lowest priority because it comes last.

This is probably part of why this value is called the “nice value”, because the greater the number the “nicer” is the process when it comes to demanding resources. A process with the value of 19 is the nicest because it is the least selfish, so to speak.

The nice command allows you to start a process with a particular nice value, setting the process priority, whereas the renice command allows changing the nice value of an already running process.

nice

To start a process with a custom nice value you run the desired command prefixed by the appropriate nice command, like this:

nice -n 10 znc

So the -n option says we want to adjust the nice value, the 10 is the actual value, and znc is the command in this example. This will start the znc process with the nice value of 10, a fairly low priority.

Now if you use the ps command, which lists running processes, to search for a znc process you’ll see that its nice (NI) value is 10:

ps -l -C "znc"

F S   UID   PID  PPID  C PRI  NI ADDR SZ WCHAN  TTY          TIME CMD
1 S  1008 13631     1  0  90  10 -  5251 -      ?        00:15:05 znc

The -l option tells it to show the process in the long format, listing all information about it, and the -C option followed by the command just tells it to look for a process started by that command.

renice

If you’ve got an already running process you can change its nice value, and therefore its priority, without restarting it. Simply run the renice command like this:

 renice -n 7 -p 13631  

So the syntax is the same except instead of specifying a command we’re specifying a process ID (PID), with the -p option. We need to have a process ID of the running process before we can renice it. You can find it in various ways, but the simplest is to just use the above mentioned ps command:

ps -l -C "znc"  

Then simply look for the PID field for the value to put after -p and you’re set.

When you run the ps command after renicing you’ll see the new NI value reflected.

The mkfs command available in UNIX and Linux operating systems is used to create file systems on various storage devices or partitions. It stands for “make filesystem”, and creating a file system is essentially an equivalent to what is popularly known as “formatting” a disk or a partition with a particular file system type (such as FAT32 or NTFS in Windows).

In other words you can use the mkfs command to format a storage device or a partition to a particular file system type, which can be ext2, ext3, ext4, FAT, NTFS, HFS, and others. This is its basic usage:

$ sudo mkfs -t type /dev/device

Where type should be replaced by the file system type such as ext3, and /dev/device by a device you want to format such as /dev/sdb1. The sudo command before mkfs just makes it run as a superuser or root, which is typically necessary when making file systems.

Here’s an example command:

$ sudo mkfs -t ext3 /dev/sdb1

This would format the device at /dev/sdb1 with an ext3 file system. Note that this will for sure delete all data you might have on that device!

If you’re not sure what device node (like /dev/sdb1) your partition or storage device is on you can run the sudo fdisk -l command to get a list that can help you determine which it is. If it is an USB stick or other external USB storage, for example, it will reside under a different letter than your internal disks.

So if your internal disk is /dev/sda (likely), and you don’t have two or more disks in your machine, then your external storage device will likely be at /dev/sdb. If you do have multiple storage devices built into your computer then they may be at /dev/sda and /dev/sdb respectively which would put any external device you connect at /dev/sdc. As for numbers, they simply represent the partition. So /dev/sdb1 is simply the first (even if only), partition on that device.

Moving back to making file sytems, you can also use shortcut commands that may be available for various file systems suck as mkfs.ext4 for ext4, mkfs.vfat for FAT, and so on. Then running a command like this..

$ sudo mkfs.ext4 /dev/sdb1

.. will have the same result as the previous example command, and will create an ext4 file system on /dev/sdb1, which in this example happens to be an USB flash drive.

Finally, if you receive a message telling you that the device is mounted and it will not make a file system on it you will need to unmount it using the umount command like this:

$ sudo umount /dev/sdb1

And then you can proceed with formatting as shown above.

See Also

• mkfs command in Unix
• advanced commands in Unix

In UNIX and Linux operating systems everything resides in a tree like structure rooted at /, the root directory. This includes storage devices with partitions and their own file systems. The mount command mounts these somewhere within this tree structure. For instance, a disk partition used for data storage can be mounted on /mnt/data or /media/data or wherever else you find it convenient or prudent.

The mount command accepts options that determine how is the file system mounted. A basic mount command without any options can be as simple as this:

sudo mount /dev/sdb1 /media/usb

Of course the directory you’re mounting to (in this example /media/usb) should exist beforehand. To unmount the device from it, thereby removing its file system from the file tree, just use the umount command the same way.

To mount a file system with options pass the -o option first followed by a comma separated list of mounting options, which may look something like this:

sudo mount -o noexec,auto /dev/sdb1 /media/usb/

In this case we’ve used the noexec and auto options, but we might have as well specified any number of other options depending on our needs and desires. Here is a quick overview of those you might find most useful, depending on the situation. They can be used alone or in combination with each other.

defaults

The defaults option is actually a shortcut to a number of different options that you’ll likely want if you have nothing specific in mind, and just want to mount a file system for normal use. They include rw, suid, dev, exec, auto, nouser, and async. In other words running..

sudo mount -o defaults /dev/sdb1 /media/usb  

..is the same as running..

sudo mount -o rw,suid,dev,exec,auto,nouser,async /dev/sdb1 /media/usb 

So what does each of these options mean?

rw – mount with both read and write access

suid – allows giving users who don’t own a specific file in a file system temporary permissions for running the file as if they did own it. In other words the owning user can give other users temporary permissions. This makes commands like passwd and ping usable for normal users even though their operation requires actions which normal users typically don’t have access to.

dev – allows creating devices nodes such as /dev/sdc1 within a mounted file system. The opposite option, nodev, would disallow this.

exec – allows executing binaries within the mounted file system. The opposite option, noexec, would make it impossible to execute programs from the mounted device.

auto – specifies that this file system will be automatically mounted on system startup or by running the mount -a command.

nouser – disallows the ordinary non-root user to mount this file system.

async – specifies that all input and output to the file system should be asynchronous as opposed to sync which would make them synchronous. The difference is that the asynchronous mode allows processing to run even as I/O operations are still ongoing rather than wait for them to finish, which makes sense most of the time, and is therefore a reasonable default option.

If all of these options sound fine to your specific need then just passing the defaults option will be good. However, if you don’t want one or more of these default options you may want to specify your own list, or use defaults with overriding subsequent options.

Here are some of the other useful options you might want to consider, some of which override or are the opposite of the above defaults, but could be useful in certain situations.

ro – mounts the file system as read-only, disallowing any write access to the mounted file system. This could be useful if you want to make sure to preserve the data on the file system as is, and especially prevent overwriting any data, when you are mounting the file system only for the purpose of accessing the files on it.

noexec – disallows executing binaries on the mounted file system, which could also be used for file systems used only as data storage where you don’t wish programs to run.

users – makes it possible for every user on the system to mount or unmount the file system.

group – allows non-root users to mount the file system if one of their groups is the same as the group to which the device belongs.

remount – useful when you want to mount an already mounted file system, but with different options than those specified previously or within the /etc/fstab configuration file, and without changing the mount point (the path where it is mounted).

noatime – prevents updating access times on inodes of the file system, which could speed up access on a frequently accessed file system for a specialized purpose.

umount options

Finally, you can pass the same options to the umount command using the -O option first, like this:

umount -O noexec /dev/sdb1 

Options passed to the umount command only mean that the command will apply to file systems which have the specified option within the /etc/fstab configuration file. In the above example it will not apply if /dev/sdb1 has no noexec option specified in /etc/fstab.