常用的vps突然ssh连不上了，通过管理网页的web vnc 连接后，发现ssh 命令出问题，连带scp也不行。联系客服，不给解决。在网上搜到如下文章，解决了问题。
检查过程中几点发现：
1，/var/log/messages 内容被清空
2，之前大意将jupyter notebook放在后台运行，是个弱密码，端口号也不生僻，看后台日志，有俄罗斯的ip访问，以及异常网址，访问过去发现是个攻击性的PHP
This issue has been resolved. Here are the commands I ran to get it resolved.
Pastebin of "ssh -v `host' " http://paste.ubuntu.com/57704/ dmesg /var/log/auth.log http://paste.ubuntu.com/57707 sudo /etc/init.d/ssh restart OUTPUT: Could not load host key: /etc/ssh/ssh_host_key disabiling protocol version 1. Could not load host key Missing privilege separation directory: /var/empty sudo apt-get remove --purge openssh-server && sudo apt-get install openssh-server OUTPUT: Errors were encountered while processing: /var/cache/apt/archives/openssh-server_1%3a4.7pl-8ubuntu1.2_i386.deb E: Sub process /usr/bin/dpkg returned an error code (1) sudo dpkg -i /var/cache/apt/archives/openssh-server_1%3a4.7pl-8ubuntu1.2_i386.deb OUTPUT: Unable to make backup link of `./usr/sbin/sshd' before installing new version: Operation not permitted sudo -i then dpkg -i /var/cache/apt/archives/openssh-server_1%3a4.7pl-8ubuntu1.2_i386.deb OUTPUT: dpkg: error processing /var/cache/apt/archives/openssh-server_1%3a4.7pl-8ubuntu1.2_i386.deb (--install): cannot access archive: No such file or directory sudo apt-get install openssh-server OUTPUT: dpkg: error processing /var/cache/apt/archives/openssh-server_1%3a4.7p1-8ubuntu1.2_i386.deb (--unpack): unable to make backup link of `./usr/sbin/sshd' before installing new version: Operation not permitted dmesg http://paste.ubuntu.com/57718/ sudo dpkg --purge openssh-server OUTPUT: dpkg - warning: ignoring request to remove openssh-server which isn't installed ls -l /usr/sbin/sshd OUTPUT: -rwxr-xr-x 1 root root 236456 2007-03-23 14:29 /usr/sbin/sshd lsattr /usr/sbin/sshd OUTPUT: su--ia------------ /usr/sbin/sshd chattr -i /usr/sbin/sshd sudo apt-get install openssh-server OUTPUT: dpkg: error processing /var/cache/apt/archives/openssh-server_1%3a4.7p1-8ubuntu1.2_i386.deb (--unpack): unable to make backup link of `./usr/sbin/sshd' before installing new version: Operation not permitted sudo rm /usr/sbin/sshd OUTPUT: rm: cannot remove `/usr/sbin/sshd': Operation not permitted sudo /etc/init.d/ssh stop OUTPUT: sudo: /etc/init.d/ssh: command not found sudo killall -9 sshd OUTPUT: sshd: no process killed **REBOOT SYstem** sudo apt-get clean md5sum /usr/sbin/sshd OUTPUT: 77fc5d90723430d090144fcbaaacce7b /usr/sbin/sshd lsattr /usr/sbin/sshd OUTPUT: su---a------------ /usr/sbin/sshd chattr -a -u -s /usr/sbin/sshd mv /usr/sbin/sshd /usr/sbin/sshd.bak sudo apt-get install openssh-server rm /usr/sbin/sshd.bak md5sum /usr/sbin/sshd OUTPUT: f5e43bdf79235f04cfe09b2eb0e87a00 /usr/sbin/sshd sudo /etc/init.d/ssh restart sudo dpkg --purge openssh-client OUTPUT: dpkg: dependency problems prevent removal of openssh-client: openssh-server depends on openssh-client (= 1:4.7p1-8ubuntu1.2). autossh depends on openssh-client | ssh-client; however: Package openssh-client is to be removed. Package ssh-client is not installed. Package openssh-client which provides ssh-client is to be removed. ssh depends on openssh-client. autossh depends on openssh-client | ssh-client; however: Package openssh-client is to be removed. Package ssh-client is not installed. Package openssh-client which provides ssh-client is to be removed. dpkg: error processing openssh-client (--purge): dependency problems - not removing Errors were encountered while processing: openssh-client sudo dpkg --purge --force-all openssh-client sudo apt-get install openssh-client OUTPUT: dpkg: error processing /var/cache/apt/archives/openssh-client_1%3a4.7p1-8ubuntu1.2_i386.deb (--unpack): unable to make backup link of `./usr/bin/ssh' before installing new version: Operation not permitted dpkg-deb: subprocess paste killed by signal (broken pipe) Errors were encountered while processing: /var/cache/apt/archives/openssh-client_1%3a4.7p1-8ubuntu1.2_i386.deb E: Sub-process /usr/bin/dpkg returned an error code (1) sudo lsattr /usr/bin/ssh OUTPUT: su--ia------------ /usr/bin/ssh sudo chattr -i -a /usr/bin/ssh sudo mv /usr/bin/ssh /usr/bin/ssh.bak sudo apt-get install openssh-client OUTPUT: dpkg: error processing /var/cache/apt/archives/openssh-client_1%3a4.7p1-8ubuntu1.2_i386.deb (--unpack): unable to make backup link of `./usr/bin/scp' before installing new version: Operation not permitted dpkg-deb: subprocess paste killed by signal (broken pipe) Errors were encountered while processing: /var/cache/apt/archives/openssh-client_1%3a4.7p1-8ubuntu1.2_i386.deb E: Sub-process /usr/bin/dpkg returned an error code (1) sudo rm /usr/bin/ssh.bak sudo chattr -i -a scp && sudo chattr -i -a sftp sudo apt-get install openssh-client sudo ssh-vulnkey (2 keys in output; not blacklisted) ssh-vulnkey (same 2 keys; not blacklisted) Finished off with " sudo touch /forcefsck " to check my filesystem