pstack和dmesg

活着的时候用pstack，死了看dmesg，让我们看看pstack的样子吧：

[[email protected] ~]$ which pstack
/usr/bin/pstack
[[email protected] ~]$ file /usr/bin/pstack
/usr/bin/pstack: symbolic link to `gstack'
[[email protected] ~]$ which gstack
/usr/bin/gstack
[[email protected] ~]$ file /usr/bin/gstack
/usr/bin/gstack: POSIX shell script, ASCII text executable
[[email protected] ~]$ more /usr/bin/gstack
#!/bin/sh

if test $# -ne 1; then
    echo "Usage: `basename $0 .sh` <process-id>" 1>&2
    exit 1
fi

if test ! -r /proc/$1; then
    echo "Process $1 not found." 1>&2
    exit 1
fi

# GDB doesn't allow "thread apply all bt" when the process isn't
# threaded; need to peek at the process to determine if that or the
# simpler "bt" should be used.

backtrace="bt"
if test -d /proc/$1/task ; then
    # Newer kernel; has a task/ directory.
    if test `/bin/ls /proc/$1/task | /usr/bin/wc -l` -gt 1 2>/dev/null ; then
	backtrace="thread apply all bt"
    fi
elif test -f /proc/$1/maps ; then
    # Older kernel; go by it loading libpthread.
    if /bin/grep -e libpthread /proc/$1/maps > /dev/null 2>&1 ; then
	backtrace="thread apply all bt"
    fi
fi

GDB=${GDB:-/usr/bin/gdb}

# Run GDB, strip out unwanted noise.
# --readnever is no longer used since .gdb_index is now in use.
$GDB --quiet -nx $GDBARGS /proc/$1/exe $1 <<EOF 2>&1 | 
set width 0
set height 0
set pagination no
$backtrace
EOF
/bin/sed -n \
    -e 's/^\((gdb) \)*//' \
    -e '/^#/p' \
    -e '/^Thread/p'
[[email protected] ~]$ which dmesg
/usr/bin/dmesg
[[email protected] ~]$ file /usr/bin/dmesg
/usr/bin/dmesg: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.32, BuildID[sha1]=8b0c53b5d6f76a923ef6b22a266719fd3ab0eb5b, stripped