linux输入yum后提示： -bash: /usr/bin/yum: No such file or director

yum remove yum

[root@localhost ~]# yum 
-bash: /usr/bin/yum: No such file or directory 

rpm -ivh --nodeps http://mirrors.163.com/centos/5/os/x86_64/CentOS/yum-fastestmirror-1.1.16-14.el5.centos.1.noarch.rpm 
rpm -ivh --nodeps http://mirrors.163.com/centos/5/os/x86_64/CentOS/yum-metadata-parser-1.1.2-3.el5.centos.x86_64.rpm 
rpm -ivh --nodeps http://mirrors.163.com/centos/5/os/x86_64/CentOS/yum-3.2.22-26.el5.centos.noarch.rpm

--nodeps             don't verify package dependencies 

[root@localhost ~]# yum 
 There was a problem importing one of the Python modules 
 required to run yum. The error leading to this problem was: 
 
 libxml2.so.2: cannot open shared object file: No such file or directory 
 
 Please install a package which provides this module, or 
 verify that the module is installed correctly. 
 
 It's possible that the above module doesn't match the 
 current version of Python, which is: 
 2.4.3 (#1, Nov 11 2010, 13:30:19) 
 [GCC 4.1.2 20080704 (Red Hat 4.1.2-48)] 
 
 If you cannot solve this problem yourself, please go to 
 the yum faq at: 
 http://wiki.linux.duke.edu/YumFaq

[root@localhost~]# python 
 Python 2.4.3 (#1, Nov 11 2010, 13:30:19) 
 [GCC 4.1.2 20080704 (Red Hat 4.1.2-48)] on linux2 
 Type "help", "copyright", "credits" or "license" for more information. 
 >>> import yum 
 Traceback (most recent call last): 
  File "<stdin>", line 1, in ? 
  File "/usr/lib/python2.4/site-packages/yum/__init__.py", line 54, in ? 
   import transactioninfo 
  File "/usr/lib/python2.4/site-packages/yum/transactioninfo.py", line 31, in ? 
   from sqlitesack import YumAvailablePackageSqlite 
  File "/usr/lib/python2.4/site-packages/yum/sqlitesack.py", line 26, in ? 
   import yumRepo 
  File "/usr/lib/python2.4/site-packages/yum/yumRepo.py", line 32, in ? 
   import sqlitecachec 
  File "/usr/lib64/python2.4/site-packages/sqlitecachec.py", line 19, in ? 
   import _sqlitecache 
 ImportError: libxml2.so.2: cannot open shared object file: No such file or directory 
 >>>

rpm -ivh http://mirrors.163.com/centos/5/os/x86_64/CentOS/libxml2-2.6.26-2.1.2.8.x86_64.rpm

[root@localhost ~]# yum 
 Loaded plugins: fastestmirror 
 You need to give some command 
 usage: yum [options] COMMAND 
 
 List of Commands: 
 
 check-update  Check for available package updates 
 clean     Remove cached data 
 deplist    List a package's dependencies 
 downgrade   downgrade a package 
 erase     Remove a package or packages from your system 
 groupinfo   Display details about a package group 
 groupinstall  Install the packages in a group on your system 
 grouplist   List available package groups 
 groupremove  Remove the packages in a group from your system 
 help      Display a helpful usage message 
 info      Display details about a package or group of packages 
 install    Install a package or packages on your system 
 list      List a package or groups of packages 
 localinstall  Install a local RPM 
 makecache   Generate the metadata cache 
 provides    Find what package provides the given value 
 reinstall   reinstall a package 
 repolist    Display the configured software repositories 
 resolvedep   Determine which package provides the given dependency 
 search     Search package details for the given string 
 shell     Run an interactive yum shell 
 update     Update a package or packages on your system 
 upgrade    Update packages taking obsoletes into account 
 
 
 options: 
  -h, --help      show this help message and exit 
  -t, --tolerant    be tolerant of errors 
  -C          run entirely from cache, don't update cache 
  -c [config file]   config file location 
  -R [minutes]     maximum command wait time 
  -d [debug level]   debugging output level 
  --showduplicates   show duplicates, in repos, in list/search commands 
  -e [error level]   error output level 
  -q, --quiet      quiet operation 
  -v, --verbose     verbose operation 
  -y          answer yes for all questions 
  --version       show Yum version and exit 
  --installroot=[path] set install root 
  --enablerepo=[repo]  enable one or more repositories (wildcards allowed) 
  --disablerepo=[repo] disable one or more repositories (wildcards allowed) 
  -x [package], --exclude=[package] 
             exclude package(s) by name or glob 
  --disableexcludes=[repo] 
             disable exclude from main, for a repo or for 
             everything 
  --obsoletes      enable obsoletes processing during updates 
  --noplugins      disable Yum plugins 
  --nogpgcheck     disable gpg signature checking 
  --disableplugin=[plugin] 
             disable plugins by name 
  --enableplugin=[plugin] 
             enable plugins by name 
  --skip-broken     skip packages with depsolving problems 
  --color=COLOR     control whether color is used 
 
  Plugin Options:

yum update