我想为几个人运行一个老式的外壳服务器。一种使用户可以通过ssh访问的方式，以便他们可以运行软件（自己的或提供的）。我关心的是用户之间的适当隔离。

我不希望他们查看彼此的进程，访问彼此的文件（除非明确允许），等等。最好不要被每个特权升级错误所咬住或在每次较小的内核更新时重新启动服务器。采取这些安全措施后，保持运行常规服务（如Web和邮件托管）的选项将是非常理想的。

早在我使用grsec的那一天，但这需要保留在较旧的内核上，并要自己处理编译它的麻烦。有没有更现代，更Ubuntu的方法来确保共享服务器上的用户分离？

也许您可以使用AppArmor做到这一点？也许有一个为共享环境预配置的内核存储库？还是基于容器的解决方案？这些最近很流行。

hidepid

procfs在Linux上现在支持该hidepid选项。来自man 5 proc：

hidepid=n (since Linux 3.3)
      This   option   controls  who  can  access  the  information  in
      /proc/[pid]  directories.   The  argument,  n,  is  one  of  the
      following values:

      0   Everybody  may  access all /proc/[pid] directories.  This is
          the traditional behavior, and  the  default  if  this  mount
          option is not specified.

      1   Users  may  not  access  files and subdirectories inside any
          /proc/[pid]  directories  but  their  own  (the  /proc/[pid]
          directories  themselves  remain  visible).   Sensitive files
          such as /proc/[pid]/cmdline and /proc/[pid]/status  are  now
          protected  against other users.  This makes it impossible to
          learn whether any user is running  a  specific  program  (so
          long  as  the program doesn't otherwise reveal itself by its
          behavior).

      2   As for mode 1, but in addition the  /proc/[pid]  directories
          belonging  to other users become invisible.  This means that
          /proc/[pid] entries can no longer be used  to  discover  the
          PIDs  on  the  system.   This  doesn't  hide the fact that a
          process with a specific PID value exists (it can be  learned
          by  other  means,  for  example,  by "kill -0 $PID"), but it
          hides a process's UID and  GID,  which  could  otherwise  be
          learned  by  employing  stat(2)  on a /proc/[pid] directory.
          This greatly complicates an  attacker's  task  of  gathering
          information   about  running  processes  (e.g.,  discovering
          whether some daemon is  running  with  elevated  privileges,
          whether  another  user  is  running  some sensitive program,
          whether other users are running any program at all,  and  so
          on).

gid=gid (since Linux 3.3)
      Specifies  the  ID  of  a  group whose members are authorized to
      learn  process  information  otherwise  prohibited  by   hidepid
      (ie/e/,  users  in this group behave as though /proc was mounted
      with hidepid=0.  This group should be used instead of approaches
      such as putting nonroot users into the sudoers(5) file.

因此，安装/proc有hidepid=2足够隐藏其他用户在Linux上> 3.3过程的细节。Ubuntu 12.04默认带有3.2，但是您可以安装较新的内核。Ubuntu 14.04及更高版本很容易满足此要求。

访问控制列表

第一步，rwx从每个主目录中除去对其他人的权限（如果需要，还应除去对组的权限）。我当然假设包含主目录的文件夹对除root以外的任何人都没有写权限。

然后，使用ACL授予Web服务器和邮件服务器等服务对相应目录的访问权限。例如，要授予Web服务器进程对用户主页的访问权限，假设www-data是用户，并且~/public_html是主页的保存位置：

setfacl u:www-data:X ~user
setfacl d:u:www-data:rX ~user/public_html

同样，为邮件过程和邮箱目录添加ACL。

默认情况下，至少在Ubuntu 14.04及更高版本上，在ext4上默认启用ACL。

/tmp 和 umask

另一个问题是/tmp。设置，umask使文件无法在组或世界范围内读取，从而使其他用户无法访问用户的临时文件。

使用这三个设置，用户将无法访问其他用户的文件或检查他们的进程。