Mknod


 
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Operating Systems HP-UX Mknod
# 1  
Old 05-26-2008
Mknod

Hey guys i dont quite understand mknod, can anyone explain it to me and what is its purpose in LVM.
# 2  
Old 05-26-2008
Mknod

Quote:
Originally Posted by sbn
Hey guys i dont quite understand mknod, can anyone explain it to me and what is its purpose in LVM.

Hello,

mknod - create special files
SYNOPSIS

/sbin/mknod name c major minor

/sbin/mknod name b major minor

/sbin/mknod name p
DESCRIPTION

The mknod command creates the following types of files:

*

Character device special file (first SYNOPSIS form),
*

Block device special file (second SYNOPSIS form),
*

FIFO file, sometimes called a named pipe (third SYNOPSIS form).

name is the path name of the file to be created. The newly created file has a default mode that is readable and writable by all users (0666), but the mode is modified by the current setting of the user's file mode creation mask (see umask(1)).
Character and Block Special Files

Character device special files are used for devices that can transfer single bytes at a time, such as nine-track magnetic tape drives, printers, plotters, disk drives operating in "raw" mode, and terminals. To create a character special file, use the c argument.

Block device special files are used for devices that usually transfer a block of data at a time, such as disk drives. To create a block device special file, use the b argument.

The remaining arguments specify the device that will be accessible through the new special file:

major

The major number specifies the major device type (for example, the device driver number).
minor

The minor number specifies the device location, which is typically, but not always, the unit, drive, and/or line number.

The major and minor values can each be specified in hexadecimal, octal, or decimal, using C language conventions (decimal: no leading zero; octal: leading zero; hexadecimal: leading 0x).

The assignment of major and minor device numbers is specific to each HP-UX system. Refer to the System Administrator manuals supplied with your system for details.

Only users who have appropriate privileges can use mknod to create a character or block device special file.
FIFO files

To create a FIFO (named pipe or buffer) file, use the p argument. You can also use the mkfifo command for this purpose (see mkfifo(1)). All users can use mknod to create FIFO files.
WARNINGS

Access Control Lists

In HFS file systems, optional ACL entries can be added to special files and FIFOs with the chacl command (see chacl(1)). In JFS file systems, optional ACL entries can be added to special files and FIFOs with the setacl command (see setacl(1)). However, system programs are likely to silently change or eliminate the optional ACL entries for these files.

Regards
# 3  
Old 05-27-2008
ok so the command

mknod /dev/vg01/group c 64 0x010001 creates a character file type group.

and in LVM in using this mknod /dev/vg01/group c 64 0x010001 is it always necessary that the file name to be created is group? or can i use other filenames.
# 4  
Old 05-27-2008
mknod is a utility to make filesystem objects. In the case of LVM you might do:
mknod /dev/vgxyz/group c 64 0x030000

You can call a volume group vgxyz if you want, but you must have a file called "group" in it. This form of mknod is making a character special file. 64 is the number of the LVM driver. (lsdev can list drivers.) 0x030000 is a unique number that you must pick to identify the volume group to the kernel. To you it's the vgxyz volume group, but to the kernel, it's the 03 volume group. The group file connects /dev/xyz to the number 03. Anytime you do a vgchange or whatever, the vgchange command needs to let the kernel know what's happening and it talks to the group file to do that.

Cameron, you should be using mkfifo to make your fifo's. And fifo's (aka named pipes) have nothing to do with this.
# 5  
Old 05-28-2008
Thanks for all for the info...
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