John the Ripper免费的开源软件，是一个快速的密码破解工具，用于在已知密文的情况下尝试破解出明文的破解密码软件，支持大多数的加密算法，如DES、MD4、MD5等。它支持多种不同类型的系统架构，包括Unix、Linux、Windows、DOS模式、BeOS和OpenVMS，主要目的是破解不够牢固的Unix/Linux系统密码。
----摘自百度百科
首先通过官网https://www.openwall.com/john/ 下载源码包,解压并编译安装
wget http://www.openwall.com/john/j/john-1.8.0.tar.gz
tar -zxvf john-1.8.0.tar.gz
cd john-1.9.0-jumbo-1/src/
make
To build John the Ripper, type:
make clean SYSTEM
where SYSTEM can be one of the following:
linux-x86-64-avx Linux, x86-64 with AVX (2011+ Intel CPUs)
linux-x86-64-xop Linux, x86-64 with AVX and XOP (2011+ AMD CPUs)
linux-x86-64 Linux, x86-64 with SSE2 (most common)
linux-x86-avx Linux, x86 32-bit with AVX (2011+ Intel CPUs)
linux-x86-xop Linux, x86 32-bit with AVX and XOP (2011+ AMD CPUs)
linux-x86-sse2 Linux, x86 32-bit with SSE2 (most common, if 32-bit)
linux-x86-mmx Linux, x86 32-bit with MMX (for old computers)
linux-x86-any Linux, x86 32-bit (for truly ancient computers)
linux-alpha Linux, Alpha
linux-sparc Linux, SPARC 32-bit
linux-ppc32-altivec Linux, PowerPC w/AltiVec (best)
linux-ppc32 Linux, PowerPC 32-bit
linux-ppc64 Linux, PowerPC 64-bit
linux-ia64 Linux, IA-64
freebsd-x86-64 FreeBSD, x86-64 with SSE2 (best)
freebsd-x86-sse2 FreeBSD, x86 with SSE2 (best if 32-bit)
freebsd-x86-mmx FreeBSD, x86 with MMX
freebsd-x86-any FreeBSD, x86
freebsd-alpha FreeBSD, Alpha
openbsd-x86-64 OpenBSD, x86-64 with SSE2 (best)
openbsd-x86-sse2 OpenBSD, x86 with SSE2 (best if 32-bit)
openbsd-x86-mmx OpenBSD, x86 with MMX
openbsd-x86-any OpenBSD, x86
openbsd-alpha OpenBSD, Alpha
openbsd-sparc64 OpenBSD, SPARC 64-bit (best)
openbsd-sparc OpenBSD, SPARC 32-bit
openbsd-ppc32 OpenBSD, PowerPC 32-bit
openbsd-ppc64 OpenBSD, PowerPC 64-bit
openbsd-pa-risc OpenBSD, PA-RISC
openbsd-vax OpenBSD, VAX
netbsd-sparc64 NetBSD, SPARC 64-bit
netbsd-vax NetBSD, VAX
solaris-sparc64-cc Solaris, SPARC V9 64-bit, cc (best)
solaris-sparc64-gcc Solaris, SPARC V9 64-bit, gcc
solaris-sparcv9-cc Solaris, SPARC V9 32-bit, cc
solaris-sparcv8-cc Solaris, SPARC V8 32-bit, cc
solaris-sparc-gcc Solaris, SPARC 32-bit, gcc
solaris-x86-64-cc Solaris, x86-64 with SSE2, cc (best)
solaris-x86-64-gcc Solaris, x86-64 with SSE2, gcc
solaris-x86-sse2-cc Solaris 9 4/04+, x86 with SSE2, cc
solaris-x86-sse2-gcc Solaris 9 4/04+, x86 with SSE2, gcc
solaris-x86-mmx-cc Solaris, x86 with MMX, cc
solaris-x86-mmx-gcc Solaris, x86 with MMX, gcc
solaris-x86-any-cc Solaris, x86, cc
solaris-x86-any-gcc Solaris, x86, gcc
sco-x86-any-gcc SCO, x86, gcc
sco-x86-any-cc SCO, x86, cc
tru64-alpha Tru64 (Digital UNIX, OSF/1), Alpha
aix-ppc32 AIX, PowerPC 32-bit
macosx-x86-64 Mac OS X 10.5+, Xcode 3.0+, x86-64 with SSE2 (best)
macosx-x86-sse2 Mac OS X, x86 with SSE2
macosx-ppc32-altivec Mac OS X, PowerPC w/AltiVec (best)
macosx-ppc32 Mac OS X, PowerPC 32-bit
macosx-ppc64 Mac OS X 10.4+, PowerPC 64-bit
macosx-universal Mac OS X, Universal Binary (x86 + x86-64 + PPC)
hpux-pa-risc-gcc HP-UX, PA-RISC, gcc
hpux-pa-risc-cc HP-UX, PA-RISC, ANSI cc
irix-mips64-r10k IRIX, MIPS 64-bit (R10K) (best)
irix-mips64 IRIX, MIPS 64-bit
irix-mips32 IRIX, MIPS 32-bit
dos-djgpp-x86-mmx DOS, DJGPP, x86 with MMX
dos-djgpp-x86-any DOS, DJGPP, x86
win32-cygwin-x86-sse2 Win32, Cygwin, x86 with SSE2 (best)
win32-cygwin-x86-mmx Win32, Cygwin, x86 with MMX
win32-cygwin-x86-any Win32, Cygwin, x86
beos-x86-sse2 BeOS, x86 with SSE2 (best)
beos-x86-mmx BeOS, x86 with MMX
beos-x86-any BeOS, x86
generic Any other Unix-like system with gcc
make clean linux-x86-64安装完毕后 ,cd 到run目录下，"./john --single /etc/shadow 测试，john会把最终结果输出到john.pot中，要尽快删除哦
[root@liukai run]# ./john --single /etc/shadow
Loaded 4 password hashes with 4 different salts (crypt, generic crypt(3) [?/64])
Press 'q' or Ctrl-C to abort, almost any other key for status
liukai (liu)
liukai (liu1)
liukai (liu2)
3g 0:00:00:09 100% 0.3099g/s 329.9p/s 330.4c/s 330.4C/s root999991907..999991900
Use the "--show" option to display all of the cracked passwords reliably
Session completed
通过爆破检测自己的用户是否把密码设的足够安全，是很有必要的。