Working with the Unix OS

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Processes II time_t msg_rtime; /* time of last msgrcv */ time_t msg_ctime; /* time of last msgctl */ /* that changed the above */ } ! Message queue structures in kernel msqid msg-perrn msg_first msg_last … … msg_ctime link type=100 length=l data_ link type=200 length=2 data_ link type=300 length=3 data A new message is created, or an existing message queue is accessed with msgget system call. int msgget(key_t key, int msgflag); msgflag 0400 MSG_R read by owner 0200 MSG_W write by owner 0040 MSG_R >> 3 read by group 0020 MSG_W >> 3 write by group 0004 MSG_R >> 6 read by world 0002 MSG_W >> 6 write by world IPC_CREAT & IPC_EXCL #include #include #include int msgsnd(int msqid, struct msgbuf *ptr, int length, int flag); struct msgbuf { long mtype; /* message type, must be > 0 */ char mtext[l]; /* message data */ ; } - The data mtext can be binary data or text. - The kernel does not interpret the contents of the message at all, so cooperating processes could define their own structure. - The length is in bytes. - The flag can be set to IPC_NOWAIT or zero. int msgrcv(int msqid, struct msgbuf *ptr, int length, long msgtype, int flag); If MSG_NOERROR bit in flag is set, than data of received message is greater than length. specify which message on queue is returned: - if msgtype = 0 then first message on queue - if msgtype > 0 then first with a type = msgtype - if msgtype < 0 then first message with lowest type
Processes II int msgctl(int msqid, int crod, struct msqid_ds *buff); cmd of IPC_RMID to remove message queue from system Multiplexed Messages client 1 pid=123 client 21 pid=456 client 3 pid=789 type=1 123 1 456 1 789 type=123/456/789 1 server message queue Features: - read in any order - assign priorities - read any message Semaphores Semaphores are a synchronization primitive. We will use to synchronize access to shared memory segments. A semaphore is a integer resource counter. If we have one resource, a shared file, then valid values are 0 & 1. process A process B kernel semaphore: 0 or 1 Since our use of semaphores is to provide resource synchronization between different processes, the semaphore value must be stored in the kernel. To obtain a resource that is controlled by a semaphore, a process needs to test its current value, and if value> 0, decrement the value by 1. If value = 0, the process must wait until value> 0 (wait for some other process to release resource). To release resource, a process increments the value. System V implementation of semaphores is done in the kernel - guarantee a group of operations is atomic. #include #include /* defines ipc-perm structure */ struct semid_ds { struct ipc-perm sem-perm; /* operation perm struct */ struct sem *sem_base; /* ptr to 1st semaphore in set */ ushort sem_nsems; /* # of semaphores in set */ time_t sem_otime; /* time of last semop */ time_t sem_ctime; /* time of last change */ }; struct sem { ushort semval; /* semaphore value, non -ve */ short sempid; /* pid of last operation */ ushort semncnt; /* # awaiting semval > cval */ ushort semzcnt; /* # awaiting semval = 0 */ }; Kernel also maintains for each value in the set: - process ID of process that did last operation - number of processes waiting for value to increase - number of processes waiting for value to = zero 138
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UNIVERSITY OF ATHENS DEPARTMENT OF
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Figure 27. Driver Entry Points.....
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Introduction to Unix ! Execution ma
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Introduction to Unix It works in th
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Introduction to Unix * matches 0 or
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Introduction to Unix vi file-name s
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Introduction to Unix 1,$s/^/>>/ 1,$
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Introduction to Unix ! Special Devi
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Introduction to Unix Working with F
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Introduction to Unix ! Communicatio
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Unix Shells 2. UNIX SHELLS Back Quo
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Unix Shells ! CASE Statement case t
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Unix Shells two lines !Y@Y@Z@Z@ZY c
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Unix Shells if $append then tee -a
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C Programming - Basics main() { int
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C Programming - Basics e.g. i += 2
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External Variables A C program cons
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C Programming - Basics main.c #incl
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C Programming - Basics default: pri
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C Programming - Basics struct tnode
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Unix Tools 4. UNIX TOOLS Tools of t
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Unix Tools Korn shell ! .profile HI
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Unix Tools grep "$name" $PHONEBOOK
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Unix Tools awk '$3 > 0 { print $1,
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Unix Tools END { print max, maxline
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Unix Tools Let an example input fil
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Unix Tools Brown eqn 1 # output Jon
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Development Tools Make looks at the
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Development Tools /* compute size o
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Development Tools #endif #line cons
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Development Tools 1.1 5 lines Retri
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Development Tools In Emacs, you may
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Development Tools */ %{ #define YYS
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C Libraries 6. C LIBRARIES Input an
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C Libraries } while (!feof(fp1)) pu
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C Libraries } free(p); /* what is w
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C Libraries } if ((fp->flag&( _READ
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C Libraries /* dirwalk: apply fcn t
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C Libraries } switch (pid=fork()){
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C Libraries What is curses? - libra
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C Libraries } if ((fd=fopen(argv[1]
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Introduction to kernel 7. INTRODUCT
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82 Introduction to kernel Programs
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Introduction to kernel } { printf("
Page 89 and 90: Introduction to kernel The kernel r
Page 91 and 92: Introduction to kernel UNIX Interna
Page 93 and 94: Introduction to kernel File System
Page 95 and 96: Introduction to kernel Every proces
Page 97 and 98: Processes I Process States 1. Execu
Page 99 and 100: Processes I } printf("%d %s\n", cnt
Page 101 and 102: Processes I dup (and other similar
Page 103 and 104: Processes I The u area contains - p
Page 105 and 106: Processes I The Context of a Proces
Page 107 and 108: Processes I Process Control use and
Page 109 and 110: Processes I Although the processes
Page 111 and 112: Processes I Handling Signals - proc
Page 113 and 114: Processes I USER=neville PATH=/user
Page 115 and 116: Processes I ! Shadow Password /etc/
Page 117 and 118: struct timeval { long tv_sec; /* se
Page 119 and 120: Processes I F_SETFL set status flag
Page 121 and 122: Processes I process is the child pr
Page 123 and 124: Processes I Rules about sharing of
Page 125 and 126: Processes II 9. PROCESSES (II) FORK
Page 127 and 128: Processes II /* background.c */ #in
Page 129 and 130: Processes II } while (1){ printf("p
Page 131 and 132: Processes II } /* child */ signal (
Page 133 and 134: Processes II int readline(int fd, c
Page 135 and 136: Processes II { } char process_name[
Page 137 and 138: Processes II - Pipe in a single pro
Page 139: Processes II System V IPC - message
Page 143 and 144: Processes II For every semop operat
Page 145 and 146: Processes II /* client loop */ mesg
Page 147 and 148: I/O Subsystem Drivers frequently sl
Page 149 and 150: I/O Subsystem Terminal Drivers - In
Page 151 and 152: I/O Subsystem Canonical Mode algori
Page 153 and 154: I/O Subsystem Raw Mode Raw mode is
Page 155 and 156: Figure 43. Pushing a Module onto a
Page 157 and 158: Interprocess Communication } { ptra
Page 159 and 160: Interprocess Communication T ID KEY
Page 161 and 162: Interprocess Communication }; int m
Page 163 and 164: Interprocess Communication for (i=0
Page 165 and 166: Interprocess Communication /* struc
Page 167 and 168: Interprocess Communication ! Compar
Page 169 and 170: … connect(sockfd,(struct sockaddr
Page 171 and 172: Interprocess Communication Address
Page 173 and 174: Process Scheduling Page Tables and
Page 176 and 177: Figure 49. Tie breaker rule Process
Page 178 and 179: Process Scheduling Clock - restart
Page 180 and 181: Process Scheduling Figure 57. Mappi
Page 182 and 183: Figure 62. Sequence of Swapping Ope
Page 184 and 185: Buffer Cache The kernel takes buffe
Page 186 and 187: Buffer Cache The kernel places the
Page 188 and 189: Buffer Cache Process B will find th
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Unix Administration 14. UNIX ADMINI
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Unix Administration Example output
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Unix Administration *) IN=-mtime -2
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Unix Administration Load /Unix kern
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Unix Administration for (i=0; i&i d
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Unix Administration fi done echo $s
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Unix Administration New Software !
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Unix Security Example: group name:g
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Unix Security $ crypt < exam320.Z >
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Unix Security - exported filesystem
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Unix Security system(cmdstr); $ ech
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Unix Security - repairs damaged use
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