CMPSC 311- Introduction to Systems Programming Module: Signals
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Systems Programming II
Systems Programming II Iqbal Mohomed CSC 209 – Summer 2004 Week 7 Motivation for Signals • When a program forks into 2 or more processes, rarely do they execute independently of each other • The processes usually require some form of synchronization, and this is typically handled using signals. Job control is another important use • Data usually needs to be passed between processes also, and this is typically handled using pipes and sockets, which we will discuss shortly • Signals are usually generated by – Machine interrupts – The program itself, other programs, or the user (i.e. from the keyboard) Introduction to Signals • When a C program receives a signal, control is immediately passed to a function called a signal handler • The signal handler function can execute some C statements and exit in three different ways: – Return control to the place in the program which was executing when the signal occurred – Return control to some other point in the program – Terminate the program by calling the exit (or _exit) function signal() • A default action is provided for each kind of signal, such as terminate, stop or ignore • For nearly all signal types, the default action can be changed using the signal() function. The exceptions are SIGKILL and SIGSTOP. The handler is defined as follows: – typedef void (*sighandler_t)(int); • To change the handler: – sighandler_t signal(int signum, sighandler_t handler); More on signal() • For each process, the OS maintains a table of actions that should be performed for each kind of signal. The signal() function changes the table entry for the signal named as the first argument to the value provided as the second argument. -
Unix/Linux Command Reference
Unix/Linux Command Reference .com File Commands System Info ls – directory listing date – show the current date and time ls -al – formatted listing with hidden files cal – show this month's calendar cd dir - change directory to dir uptime – show current uptime cd – change to home w – display who is online pwd – show current directory whoami – who you are logged in as mkdir dir – create a directory dir finger user – display information about user rm file – delete file uname -a – show kernel information rm -r dir – delete directory dir cat /proc/cpuinfo – cpu information rm -f file – force remove file cat /proc/meminfo – memory information rm -rf dir – force remove directory dir * man command – show the manual for command cp file1 file2 – copy file1 to file2 df – show disk usage cp -r dir1 dir2 – copy dir1 to dir2; create dir2 if it du – show directory space usage doesn't exist free – show memory and swap usage mv file1 file2 – rename or move file1 to file2 whereis app – show possible locations of app if file2 is an existing directory, moves file1 into which app – show which app will be run by default directory file2 ln -s file link – create symbolic link link to file Compression touch file – create or update file tar cf file.tar files – create a tar named cat > file – places standard input into file file.tar containing files more file – output the contents of file tar xf file.tar – extract the files from file.tar head file – output the first 10 lines of file tar czf file.tar.gz files – create a tar with tail file – output the last 10 lines -
Unix System Programming Overview Outline What Is a Signal? Signal
Overview Last Week: ● How to program UNIX processes (Chapters 7-9) ● fork() and exec() Unix System Programming This Week, and next week: ● UNIX inter-process communication mechanisms: signals, Signals » (next week) pipes and FIFOs. ● How to program with UNIX signals (Chapter 10) » http://en.wikipedia.org/wiki/Unix_signal ● Non-local jumps (Chapter 7) ● Focus on the sigaction() function Maria Hybinette, UGA 1 Maria Hybinette, UGA 2 Outline What is a Signal? ● A signal is an asynchronous event which is ● What is a UNIX signal? delivered to a process (instantiated by a small message) ● Signal types ● Asynchronous means that the event can occur ● Generating signals at any time (e.g., posting at a bulletin board ) ● Responding to a signal » may be unrelated to the execution of the process ● Common uses of a signal – e.g., user types Ctrl-C, or the modem hangs (SIGINT) ● Implementing a read() time-out – e.g,, user types Ctrl-Z (SIGTSTP) ● Sent from kernel (e.g. detects divide by zero ● Non-local jumps setjmp()/longjmp() (SIGFPE) or could be at the request of another ● POSIX signals process to send to another) ● Interrupted system calls ● Only information that a signal carries is its ● System calls inside handlers unique ID and that it arrived Maria Hybinette, UGA 3 Maria Hybinette, UGA 4 Signal Types (31 in POSIX) Signal Sources terminal memory ID Name Description Default Action driver management shell command 2 SIGINT Interrupt from keyboard (^C) terminate Ctr-C SIGINT SIGHUP 3 SIGQUIT Quit from keyboard (^\) terminate & core SIGSEGV 9 SIGKILL -
POSIX Signals
CSE 410: Systems Programming POSIX Signals Ethan Blanton Department of Computer Science and Engineering University at Buffalo Introduction Signals Blocking Concurrency Sending Signals Summary References POSIX Signals POSIX signals are another form of interprocess communication. They are also a way to create concurrency in programs. For these two reasons, they are rather complicated and subtle! Signals provide a simple message passing mechanism. © 2018 Ethan Blanton / CSE 410: Systems Programming Introduction Signals Blocking Concurrency Sending Signals Summary References Signals as Messages POSIX signals are asynchronous messages. Asynchronous means that their reception can occur at any time.1 The message is the reception of the signal itself. Each signal has a number, which is a small integer. POSIX signals carry no other data. 1Almost. We’ll see how to control it later. © 2018 Ethan Blanton / CSE 410: Systems Programming Introduction Signals Blocking Concurrency Sending Signals Summary References Signal Types There are two basic types of POSIX signals: Reliable signals Real-time signals Real-time signals are much more complicated. In particular, they can carry data. We will discuss only reliable signals in this lecture. © 2018 Ethan Blanton / CSE 410: Systems Programming Introduction Signals Blocking Concurrency Sending Signals Summary References Asynchronous Reception From the point of view of the application: Signals can be blocked or ignored Enabled signals may be received between any two processor instructions A received signal can run a user-defined function called a signal handler This means that enabled signals and program code must very carefully manipulate shared or global data! © 2018 Ethan Blanton / CSE 410: Systems Programming Introduction Signals Blocking Concurrency Sending Signals Summary References Signals POSIX defines a number of signals by name and number. -
Unix/Linux Command Reference
Unix/Linux Command Reference .com File Commands System Info ls – directory listing date – show the current date and time ls -al – formatted listing with hidden files cal – show this month's calendar cd dir - change directory to dir uptime – show current uptime cd – change to home w – display who is online pwd – show current directory whoami – who you are logged in as mkdir dir – create a directory dir finger user – display information about user rm file – delete file uname -a – show kernel information rm -r dir – delete directory dir cat /proc/cpuinfo – cpu information rm -f file – force remove file cat /proc/meminfo – memory information rm -rf dir – force remove directory dir * man command – show the manual for command cp file1 file2 – copy file1 to file2 df – show disk usage cp -r dir1 dir2 – copy dir1 to dir2; create dir2 if it du – show directory space usage doesn't exist free – show memory and swap usage mv file1 file2 – rename or move file1 to file2 whereis app – show possible locations of app if file2 is an existing directory, moves file1 into which app – show which app will be run by default directory file2 ln -s file link – create symbolic link link to file Compression touch file – create or update file tar cf file.tar files – create a tar named cat > file – places standard input into file file.tar containing files more file – output the contents of file tar xf file.tar – extract the files from file.tar head file – output the first 10 lines of file tar czf file.tar.gz files – create a tar with tail file – output the last 10 lines -
The Linux Command Line
The Linux Command Line Fifth Internet Edition William Shotts A LinuxCommand.org Book Copyright ©2008-2019, William E. Shotts, Jr. This work is licensed under the Creative Commons Attribution-Noncommercial-No De- rivative Works 3.0 United States License. To view a copy of this license, visit the link above or send a letter to Creative Commons, PO Box 1866, Mountain View, CA 94042. A version of this book is also available in printed form, published by No Starch Press. Copies may be purchased wherever fine books are sold. No Starch Press also offers elec- tronic formats for popular e-readers. They can be reached at: https://www.nostarch.com. Linux® is the registered trademark of Linus Torvalds. All other trademarks belong to their respective owners. This book is part of the LinuxCommand.org project, a site for Linux education and advo- cacy devoted to helping users of legacy operating systems migrate into the future. You may contact the LinuxCommand.org project at http://linuxcommand.org. Release History Version Date Description 19.01A January 28, 2019 Fifth Internet Edition (Corrected TOC) 19.01 January 17, 2019 Fifth Internet Edition. 17.10 October 19, 2017 Fourth Internet Edition. 16.07 July 28, 2016 Third Internet Edition. 13.07 July 6, 2013 Second Internet Edition. 09.12 December 14, 2009 First Internet Edition. Table of Contents Introduction....................................................................................................xvi Why Use the Command Line?......................................................................................xvi -
K15569543: Producing a TMM Diagnostic Core File
K15569543: Producing a TMM diagnostic core file Support Solution Original Publication Date: Oct 22, 2019 Update Date: Aug 12, 2020 Details Description F5 Support may ask you to produce a Traffic Management Microkernel (TMM) core file on the BIG-IP system to establish the state of TMM process during an event. You should perform this task only when asked to do so by F5 Support. Important: The BIG-IP system will temporarily fail to process traffic as it recovers from TMM restarting, and devices configured as a high availability (HA) pair may fail over. Additionally, on platforms with a large memory capacity, the system will respond slowly while it writes several gigabytes of data to the disk and compresses the core file. This process may take several minutes to complete. When the core file compression is complete, the unit returns to normal operation and restarts the TMMs. Environment BIG-IP F5 Support has requested a TMM diagnostic core file Adequate amount of disk space for the diagnostic core file K14403: Maintaining disk space on the BIG-IP system Cause None Recommended Actions To produce a TMM diagnostic core file, perform the following: 1. Disable the watchdog process K13539: Disabling the watchdog process to perform a core dump (11.x - 15.x) 2. Log in to the BIG-IP command line 3. Determine which tmm processes are running on the system, enter the following command: ps ax | grep -i tmm Note: Most BIG-IP platforms are enabled with Clustered Multiprocessing (CMP) and run multiple TMM 3. instances. Example: If a system has two instances of tmm running, output appears similar to the following: 5736 ? S 0:00 runsv tmm 12325 ? S 0:00 /usr/bin/tmipsecd --tmmcount 12 12327 ? S 0:00 /etc/bigstart/scripts/tmm.start /var/run 12 6 0 0 --platform E101 -m -s 21853 16379 ? SLl 17:22 tmm.0 -T 6 --tmid 0 --npus 12 --platform E101 -m -s 21853 16380 ? SLl 17:31 tmm.6 -T 6 --tmid 6 --npus 12 --platform E101 -m -s 21853 17707 pts/0 S+ 0:00 grep -i tmm Note: In this example, the two tmm instances are tmm.0 and tmm.6 4. -
Unix (And Linux)
AWK....................................................................................................................................4 BC .....................................................................................................................................11 CHGRP .............................................................................................................................16 CHMOD.............................................................................................................................19 CHOWN ............................................................................................................................26 CP .....................................................................................................................................29 CRON................................................................................................................................34 CSH...................................................................................................................................36 CUT...................................................................................................................................71 DATE ................................................................................................................................75 DF .....................................................................................................................................79 DIFF ..................................................................................................................................84 -
Programming with POSIX Threads II
Programming with POSIX Threads II CS 167 IV–1 Copyright © 2008 Thomas W. Doeppner. All rights reserved. Global Variables int IOfunc( ) { extern int errno; ... if (write(fd, buffer, size) == –1) { if (errno == EIO) fprintf(stderr, "IO problems ...\n"); ... return(0); } ... } CS 167 IV–2 Copyright © 2008 Thomas W. Doeppner. All rights reserved. Unix was not designed with multithreaded programming in mind. A good example of the implications of this is the manner in which error codes for failed system calls are made available to a program: if a system call fails, it returns –1 and the error code is stored in the global variable errno. Though this is not all that bad for single-threaded programs, it is plain wrong for multithreaded programs. Coping • Fix Unix’s C/system-call interface • Make errno refer to a different location in each thread – e.g. #define errno __errno(thread_ID) CS 167 IV–3 Copyright © 2008 Thomas W. Doeppner. All rights reserved. The ideal way to solve the “errno problem” would be to redesign the C/system-call interface: system calls should return only an error code. Anything else to be returned should be returned via result parameters. (This is how things are done in Windows NT.) Unfortunately, this is not possible (it would break pretty much every Unix program in existence). So we are stuck with errno. What can we do to make errno coexist with multithreaded programming? What would help would be to arrange, somehow, that each thread has its own private copy of errno. I.e., whenever a thread refers to errno, it refers to a different location from any other thread when it refers to errno. -
Linux Cheat Sheet
1 of 4 ########################################### # 1.1. File Commands. # Name: Bash CheatSheet # # # # A little overlook of the Bash basics # ls # lists your files # # ls -l # lists your files in 'long format' # Usage: A Helpful Guide # ls -a # lists all files, including hidden files # # ln -s <filename> <link> # creates symbolic link to file # Author: J. Le Coupanec # touch <filename> # creates or updates your file # Date: 2014/11/04 # cat > <filename> # places standard input into file # Edited: 2015/8/18 – Michael Stobb # more <filename> # shows the first part of a file (q to quit) ########################################### head <filename> # outputs the first 10 lines of file tail <filename> # outputs the last 10 lines of file (-f too) # 0. Shortcuts. emacs <filename> # lets you create and edit a file mv <filename1> <filename2> # moves a file cp <filename1> <filename2> # copies a file CTRL+A # move to beginning of line rm <filename> # removes a file CTRL+B # moves backward one character diff <filename1> <filename2> # compares files, and shows where differ CTRL+C # halts the current command wc <filename> # tells you how many lines, words there are CTRL+D # deletes one character backward or logs out of current session chmod -options <filename> # lets you change the permissions on files CTRL+E # moves to end of line gzip <filename> # compresses files CTRL+F # moves forward one character gunzip <filename> # uncompresses files compressed by gzip CTRL+G # aborts the current editing command and ring the terminal bell gzcat <filename> # -
POSIX Signal Handling in Java
Technical Document Series POSIX Signal Handling in Java POSIX Signal Handling In Java Introduction POSIX signals inform a running process of external events, such as the user wishing to kill the process, or the operating system signaling an impending shutdown, or the process being suspended or reinstated; or the process may have violated a resource constraint, such as excessive CPU usage or attempts to access areas outside its permitted memory space, and is asked to shutdown. In short, POSIX signals serve many different purposes. Some are even up to interpretation, such as the HUP (HangUP) signal, which is commonly used to inform a process that something about its environment has changed and the process should adjust accordingly. Some programs may interpret this to mean that the configuration has changed and needs to be reloaded; or the log file has been moved for archiving purposes and a new one should be started. The use of signals is widespread, especially on Unix-based operating systems, but Java provides no standard interface for a Java application to hear and react to them. This document shows you how to get around this limitation. The Good, the Bad, and the Ugly The good news is that there is a way to intercept POSIX signals and react to them in Java. This would allow your Java program to avoid being killable with ^C (SIGINT), for example, even ignore termination requests from the operating system (SIGTERM). Neither of these is necessarily a good idea, of course, unless you know exactly why you would want to catch these signals and either handle them yourself or ignore them altogether. -
Gist of Test Program 1 Socket Class and Its Client Class This Class Hasn't
Gist of test program 1 Socket class and its client class This class hasn't been changed except that an overloaded method send has been added. This send method use a very flexible way to send contents with a customised size, two arguments are passed, I.e. a pointer pointing to the start of the block of memory, and a integer typed size. Within this block of memory to be sent, users can send any types of data with a specified size. This is the way to make a socket send method more flexible, and more important thing is to make it type independent. Based on the same spirit, a recv method has been overloaded, with only one argument. This recv method is to receive the block of data contained in a specified memory and customised size. So the pointer will be pointing the start of the block of memory that it receives. So before sending a block of data in the memory, users should know how to package the data block. Similarly, after receiving a block of data, users should know how to decode that block of data by its types and size respectively, as shown in the figure below. Data type 1 Data type 2 Pointer pointing to start Data type ... Drawing 1: package a block of data 2 ClientSocketN class In this class, the LogSend and LogRecv methods are overloaded in order to cope with the client interface for send and recv methods described above. Again, the same type of arguments are adjusted. 3 odr.h In this header file, the ODR packet contains many things as described as follows.