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Understanding Disks and Filesystems in Unix: An Overview of Files, Directories, and More

This chapter explores the fundamentals of files and filesystems in Unix. It defines a file as a container for ordered data that persists and is accessible by name. Regular Unix files are simple sequences of bytes identified by names that resolve to their locations on disk. The chapter also covers directories, links, and devices in Unix, explaining their structures and functions. Additionally, it discusses standard directory contents and the unique `/proc` filesystem, which provides information about system processes and hardware state, including commands to navigate and retrieve data.

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Understanding Disks and Filesystems in Unix: An Overview of Files, Directories, and More

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  1. Chapter 8. Disks and Filesystems

  2. Ordinary Files • What is a file? • a container for ordered data • persistent (stays around) and accessible by name • Unix files • regular Unix files are pretty simple • essentially a sequence of bytes • Unix files are identified by a name in a directory • this name is actually used to resolve the hard disk name/number, the cylinder number, the track number, the sector, the block number • you see none of this • it allows the file to be accessed

  3. Files, Directories, Devices • Unix files come in other flavors as well, such as • Directories • a file containing pointers to other files • equivalent of a “folder” on a Mac or Windows • Links • a pointer to another file • used like the file it points to • similar to “shortcuts” in Windows, but better • Devices • access a device (like a soundcard, or mouse, or ...) like it is a file

  4. Figure 3-3 A Directory Hierarchy

  5. System Directories • Some standard directories and files in a typical Unix system • / the root • /bin BINaries (executables) used to start system • /sbin System BINaries for Superuser • /lib LIBraries used for startup • /dev DEVices (peripherals) hardware interfaces • /etc unique settings for system, config, passwds • /usr Biggest filesystem, sys tools, X, apps • /tmp temp storage, good to separate partition

  6. Typical System Directory Contents • /usr USeR stuff • /usr/bin BINaries again • /usr/include include files for compilers • /usr/lib LIBraries of functions etc. • /usr/local local stuff for apps installed later • /usr/local/bin local BINaries • /usr/local/lib local LIBraries for apps • /usr/X11R6 X window stuff • /usr/sbin sysadmin stuff • /usr/tmp place for more TeMPorary files • /var VARiable stuff—mail, print jobs, logfiles • /var/mail the mail spool • /var/log security info VERY IMPORTANT

  7. The /proc filesystem • /proc is a virtual directory. in RAM rather than in HDD. • /proc contains info about your system’s state. amount of free memory processes running external devices plugged in remaing battery power if you are working in a laptop • You can, though, navigate around it with cd command and list its contents with ls command or view some of its file contents with cat command

  8. The /proc file system • Numbers are directories representing each of the running process on the system and contain all info related to it. terra$ ls /proc/480/ auxv cwd exe maps mounts stat status wchan cmdline environ fd mem root statm task For example: cmdlinecontains the command the process started with memcontains the amount of memory this process holds • . /proc contains information about the hardware of the system cat /proc/meminfo contains information about memory state more /proc/ioports gives all the information about the availability of I/O ports on the system and the hardware device assigned to each.

  9. Figure 3-8 Inodes Each file on the disk has an inode which keeps information about the file, it’s address, etc

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