Mod 8 day 1-3 Flashcards
What is a Symbolic Link?
A symbolic link is a file containing the pathname to another file
What is a Hard Link?
A Hard Link is a pointer to a files Inode and is the same as the original file
What is a Directory Entry?
a Directory Entry is a simple data structure containing filename and Inode addresses where the files metadata can be found
What does the Touch command allow us to do?
the Touch command creates an empty file and can also alter Timestamps.
- m - modify
- a - access
- t - time
what does the Stat command allow us to do?
The stat command is used to view a file or file system status to include timestamps
What are the 3 timestamps EXT3 systems support?
- Modification-Time files data layer was last modified
- Acces- Time files data was last accessed
- Change- Time files inode (metadata layer) was last changed/created
What is an indirect pointer used for?
In your file system, if data takes up more than 12 blocks it uses a Single, Double, or Triple to alllow to go past 12 blocks of preallocated data
What is an Inode?
An Inode contains information proccesses need to access a file or metadata Contains: -file size -file ownership -file timestamp -file type -file access -number of links
What is a Data Block
A Block is a basic file allocation unit size for the EXT(x) file system and is used to store file contents
a Block is a group of consecutive sectors and can be 1024, 2048, or 4096 bytes in size.
What is a Group Descriptor Table?
A Group Descriptor Table contains:
- Starting block address of a Block Bitmap
- Starting block address of the Inode Bitmap
- Starting block address of the Inode table
- number of unallocated blocks in the group
- number of directories in the group
- unused bytes.
What is the file system that Linux uses?
Linux uses EXTx, a journaling filesystem. A journaling filesystem maintain a journal used to repair inconsistencies that may occur after an improper shutdown
What is a superblock?
A superblock is located 1024 bytes from the start of file system and is 1024 bytes in size & contains following information?
- total number of Inodes
- Total number of Blocks
- Block Size
- Number of Blocks per Group
- Number of Inodes per Block Group
- Number of reserved Blocks before the first Block Group
What is a Bitmap?
A Bitmap informs whatever is looking at it, if something is allocated or unallocated
What does the command fdisk do?
fdisk allows you to view the disks physical partitioning scheme?
What are common Virtual File Systems?
- Swapfs - used for Swapping
- Procfs - provides info for Processes
- Tmpfs - temporary file storage in memory instead of Hard disk
What are common network based file systems?
networked file systems
server message block
What are common Linux disk file systems?
EXT3, EXT4, or XFS disk file systems
What is a file system?
A File System defines the way files are stored, named, organized and accessed on a logical volume and give the OS a road map to access data on a type of file system.
What is a Kernel signal process-level interrupt?
A kernel signal is when a process commits an infraction such as division by zero
What is an Administrator Signal process-level Interrupt?
Administrator Interrupts use kill or pkill to get desired result
What is a Terminal Signal process - level interrupt?
CTRL + C & CTRL + D is to kill, interrupt or suspended processes
What is a process exception by trap?
A trap is software written to catch exceptions generated by the CPU. A trap is an error exception condition generated within the currently running process.
What is the process Exception by interrupt?
an Interrupt is a signal generated by Hardware when it wants the processors attention. An interrupt is caused by an external event & is considered asynchronous.
What are the 4 states of a process?
R- Running- Running or Runable
S- Sleeping- Waiting for resources or an event to occur
Z- Zombie- Dead Process whose process entry still exists
T- Stopped- suspended process
What is the command to check the current states of a shell process?
ps -Helf
How are processes created?
processes are created with fork(), whch creates exact copies of the original process, called a Child Process. The child may help the parent with the process. when a parent exits without waiting the child, it becomes a Zombie Process.
What is a background process?
A background process is a non-interactive, does not need user input and is not connected to a terminal. Refferred to as a daemon.
What is a foreground Process?
A Foreground Process is interactive & started by a terminal window. Normally started by a user.
What is the definition of a process? What are two types?
A process is a Program in execution.
Foreground and Background
What is the purpose of the Ulimit Command
Ulimit sets or prints the limits on shared resources for that shell.
- a -Displays limits imposed on resources
- c -Displays or set core file size
- u -Displays or sets max number of processes per user
What does the Sysctl command allow the user to do?
The Sysctl command provides an interface that allows viewing and changing kernel parameters.
- p - loads sysctl value from conf. files
- a displayes all values currently available
- w writes sysctl value for current session only
What does the commmand lsmod allow us to do?
lsmod lists currently loaded/active modules by nicely formatting the contents of /proc/modules
What is the purpose of LKMS?
The purpose of LKM (loadable kernel modules) add or remove code from the linux kernel during execution.
What is the purpose of the command Strace?
Strace is used to debug programs when the source code is unavailable
- c -count time, calls, and errors for each system call
- e traces a system call event
- o each process is written to the filename
What are the system calls for protection?
umask- sets calling process creating mask to mask
chmod- changes a files mode/permission
what are system calls for communication?
pipe - inter-process communication
mmap - creates new mapping in virtual address space
what are system calls for information?
get PID - returns PID of process
uname - returns system information
What are the system calls for process control?
fork - creates child process
wait - blocks calling process until child process exits
execve - executes program
exit - terminates process & performs cleanup
kill - sens a signal to a process to terminate it
what are system calls for file or device management?
- creat - creates & opens file
- open - opens existing file
- close - closes all file associated with terminating proc.
- read - reads data from file
- write - writes data to file
- ioctl - input/output control of device specific operation
what is the purpose of virtual file system(VFS)?
allows programs to use standard system calls to read and write to different file systems.
what is the Board Support Package(BSP)?
the BSP is essential code that allows a computer hardware device to work with computer OS
What is the purpose of Device Drivers?
a Device Driver is a low level program that allows the kernel to communicate with a specific piece of hardware.
How do I change the Service status of a script?
With the Chkconfig, service command, or running script /etc/init.d
What are the directories that have my run levels?
Run level 0 /etc/rc.d/rc0.d Run level 1 /etc/rc.d/rc1.d Run level 2 /etc/rc.d/rc2.d Run level 3 /etc/rc.d/rc3.d Run level 4 /etc/rc.d/rc4.d Run level 5 /etc/rc.d/rc5.d
what is the very first process to run on Centos6?
Initd is the first process to run on Centos6 with a PID of 1
What is the very first process to run on Centos7?
Systemd is the very first process to run on Centos7 with a PID of 1
Describe Memory Management in Linux
the Kernel manages memory normally in 4KB chunks, called pages, when pages are exhausted they are swapped, excessive swapping is called thrashing.
What is the lightweight process?
a Lightweight process (LWP) is a process that runs in user mode that runs on top of a single kernel thread & shares its address space & system resources with other lightweight processes.
Kernel Mode
The Kernel Runs in the most privileged ring
It is a privileged system area that resides between user mode & hardware platform.
How does the SCI operate?
The SCI converts a process running in user mode to a protected kernel mode process.
To implement a system call, it must transfer control through an architecture-specific feature, such a trap or interrupt.
What are the Key advantages of Linux?
- Linux is Preemptive
- Linux supports the ability to dynamically load & unload kernel
- Linux does not differentiate between threads & processes
- object oriented, plug & play, user space device file system
- free
- multi-user, multi-tasking, and protable.
What is a shell?
A shell is an interpreter and with a specific set of functions.
what are the purposes of API’s?
The purpose of APIs is to request the use of kernel services, or are referred to as a system call.
what is an application?
Applications are just computer programs that can perform certain tasks.
What is GNU C?
an Implementation of C:\ drive, library functions act as an interface for abstract system calls.
What is a windows manager?
A Windows Manager defines how the GUI environment & how the user interacts with the system.
What are the processes & threads?
The purpose of Processes & Threads is that they request kernel services.
What are the user mode components?
The user mode components are process/threads, applications, a windows manager, libraries, and other components.
What is user mode?
User applications execute in the least privlidged ring known as user mode.
What is the purpose of SUID/GUID bits?
SUID/GUID bits allow anyone to run an executable with same privileges as the owner and/or group.
What command allows you to change ownershp?
chown is how you change ownership of a file.
What is the command to change default permissions of a newly created file?
umask allows you to change default permissions of a newly created file.
What are the 3 classes of file permissions?
owner/user, group, other
How does Linux classify everything?
Linux classifies everything as a file, including directories, device files and even processes.
What are file permissions?
File permissions determine who can access system Files
