Graphics Programs Reference
In-Depth Information
reader@hacking:~/booksrc $ kill -l
1) SIGHUP 2) SIGINT 3) SIGQUIT 4) SIGILL
5) SIGTRAP 6) SIGABRT 7) SIGBUS 8) SIGFPE
9) SIGKILL 10) SIGUSR1 11) SIGSEGV 12) SIGUSR2
13) SIGPIPE 14) SIGALRM 15) SIGTERM 16) SIGSTKFLT
17) SIGCHLD 18) SIGCONT 19) SIGSTOP 20) SIGTSTP
21) SIGTTIN 22) SIGTTOU 23) SIGURG 24) SIGXCPU
25) SIGXFSZ 26) SIGVTALRM 27) SIGPROF 28) SIGWINCH
29) SIGIO 30) SIGPWR 31) SIGSYS 34) SIGRTMIN
35) SIGRTMIN+1 36) SIGRTMIN+2 37) SIGRTMIN+3 38) SIGRTMIN+4
39) SIGRTMIN+5 40) SIGRTMIN+6 41) SIGRTMIN+7 42) SIGRTMIN+8
43) SIGRTMIN+9 44) SIGRTMIN+10 45) SIGRTMIN+11 46) SIGRTMIN+12
47) SIGRTMIN+13 48) SIGRTMIN+14 49) SIGRTMIN+15 50) SIGRTMAX-14
51) SIGRTMAX-13 52) SIGRTMAX-12 53) SIGRTMAX-11 54) SIGRTMAX-10
55) SIGRTMAX-9 56) SIGRTMAX-8 57) SIGRTMAX-7 58) SIGRTMAX-6
59) SIGRTMAX-5 60) SIGRTMAX-4 61) SIGRTMAX-3 62) SIGRTMAX-2
63) SIGRTMAX-1 64) SIGRTMAX
reader@hacking:~/booksrc $ ps a | grep signal_example
24491 pts/3 R+ 0:17 ./signal_example
24512 pts/1 S+ 0:00 grep signal_example
reader@hacking:~/booksrc $ kill -10 24491
reader@hacking:~/booksrc $ kill -12 24491
reader@hacking:~/booksrc $ kill -9 24491
reader@hacking:~/booksrc $
Finally, the
SIGKILL
signal is sent using
kill -9
. This signal's handler
cannot be changed, so
kill -9
can always be used to kill processes. In the
other terminal, the running signal_example shows the signals as they are
caught and the process is killed.
reader@hacking:~/booksrc $ ./signal_example
Caught signal 10 SIGUSR1
Caught signal 12 SIGUSR2
Killed
r
eader@hacking:~/booksrc $
Signals themselves are pretty simple; however, interprocess communica-
tion can quickly become a complex web of dependencies. Fortunately, in the
new tinyweb daemon, signals are only used for clean termination, so the
implementation is simple.
0x622
Tinyweb Daemon
This newer version of the tinyweb program is a system daemon that runs in
the background without a controlling terminal. It writes its output to a log
file with timestamps, and it listens for the terminate (
SIGTERM
) signal so it
can shut down cleanly when it's killed.
These additions are fairly minor, but they provide a much more realistic
exploit target. The new portions of the code are shown in bold in the listing
below.
