![]() ![]() ![]() In this example, we used the -m option with the named pipe. Now, let’s verify that the permissions have been set properly: $ ls -l /tmp/pipe-with-permissions To understand this, let’s use the -m option to set access permissions while creating a named pipe: $ sudo mknod -m 444 /tmp/pipe-with-permissions p However, we can achieve the same result using the mknod command instead of using two separate commands. In such cases, we have to use the chmod command. Sometimes, we need to modify the access permission of the device file before using it. In this example, we can see that the /tmp/dvd-rom block device is able to access the ISO image from the CD/DVD ROM. Next, let’s mount the ISO image from the CD/DVD ROM to the /mnt directory and verify that the mount operation succeeds: $ sudo mount /tmp/dvd-rom /mnt/ Now, let’s create a new block device with the same major and minor numbers: $ sudo mknod /tmp/dvd-rom b 11 0 In the above output, we can see that its major and minor numbers are 11 and 0 respectively. Now, let’s create a new block device that behaves the same as /dev/sr0.įirst, let’s find out the major and minor numbers of the /dev/sr0: $ ls -l /dev/sr0Ĭheck Device File Major and Minor Numbers In Linux, /dev/sr0 represents the CD/DVD ROM device. To create a block device we must have to use the major and minor numbers. In addition to this, we can specify the device type as b to create a block device. It is important to note that, the newly created character device behaves like the /dev/full device because of the same major and minor numbers. Next, let’s change the file permissions: $ sudo chmod 666 /tmp/full-deviceįinally, write some data to the newly created device: $ echo "tecmint" > /tmp/full-device Now, let’s use the mknod command to create a new device that behaves the same as /dev/full device: $ sudo mknod /tmp/full-device c 1 7 To understand this, let’s write some data to this device: $ echo "" > /dev/full In Linux, the /dev/full device always returns the No space left on the device error. ![]() 1, 7 represent the major and minor numbers respectively. In the above output, the comma-separated pair of numbers i.e. Let’s use the ls command to find the major and minor numbers of the /dev/full device: $ ls -l /dev/full However, we must have to use the major and minor numbers while creating a character device. In a similar way, we can use the device type as c to create a character device. Here, we can see that the echo and cat commands are able to communicate using the named pipe. Next, let’s open another terminal and write some data to the /tmp/named-pipe file: $ echo "" > /tmp/named-pipeįinally, head over to the first terminal to view the result: View Named Pipe File Here, we can see that the cat command is waiting infinitely: Read Named Pipe File Now, let’s try to read the file: $ cat /tmp/named-pipe However, its main purpose is to allow inter-process communication between unrelated processes.įirst, let’s specify the device type as p to create a named pipe: $ mknod /tmp/named-pipe p The named pipe resides on the file system just like any other regular file. We can use the mknod command to create a named pipe. In the next example, we will see how to create a named pipe. However, this creates an unnamed pipe and its scope is limited to the current command only. Here, we have used the vertical line (|) to create a pipe. In this example, we are using the pipe to read the output of the echo command and send it as the input to the wc command for further processing. ![]() Let’s understand this with a simple example: $ echo "" | wc -c It reads the output of the previous process and sends it as the input to the next process. In Shell, the pipe is represented using the vertical line (|). In Linux, we use pipes to enable inter-process communication. We can find the reserved major and minor numbers in the Linux kernel’s documentation. In a similar way, the minor number is used to specify the actual device. This number is assigned while registering a device driver. In Linux, the major number is used to specify the device driver that needs to be used. In the above syntax, the square brackets () represent the optional arguments whereas angular brackets () represent the mandatory arguments. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |