Operating Systems 2017F: Assignment 4

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Full Questions

1. To enable public key (password-less) authentication in ssh, a user's public key should be added to what file on the remote system?
2. In ssh (on the Linux command line), in what file is a user's private key normally stored?
3. How do sshfs inode values relate to the inodes in the remotely mounted filesystem?
4. What lines in memoryll determine the inode numbers?
5. In sshfs, do a file's uid and gid values come from the remote server or from the mounting user's uid and gid?
6. What permissions does a process require for regular file access?
7. In sshfs, what determines whether a file operation is allowed or not, the remote ssh daemon, the remote kernel, the local kernel, or the local ssh process?
8. When you run fusermount via execve, what euid does fusermount's process have?
9. What environment variable allows ssh to connect to the local authentication agent?
10. Why must ssh private keys only be readable by the owner?
11. How do you control how many bytes dd writes with each write system call?
12. When you make a write system call to a file on a sshfs-mounted filesystem, how many additional write (or writev) system calls must be executed, and what processes make those system calls?

Multiple Choice

1. To enable public key (password-less) authentication in ssh, a user's public key should be added to what file on the remote system?
   1. /etc/passwd
   2. ~/.ssh/authorized_keys
   3. ~/.ssh/known_hosts
   4. ~/.ssh/id_rsa.pub
2. In ssh (on the Linux command line), in what file is a user's private key normally stored?
3. How do sshfs inode values relate to the inodes in the remotely mounted filesystem?
4. What lines in memoryll determine the inode numbers?
5. In sshfs, do a file's uid and gid values come from the remote server or from the mounting user's uid and gid?
6. What permissions does a process require for regular file access?
7. In sshfs, what determines whether a file operation is allowed or not, the remote ssh daemon, the remote kernel, the local kernel, or the local ssh process?
8. When you run fusermount via execve, what euid does fusermount's process have?
9. What environment variable allows ssh to connect to the local authentication agent?
10. Why must ssh private keys only be readable by the owner?
11. How do you control how many bytes dd writes with each write system call?
12. When you make a write system call to a file on a sshfs-mounted filesystem, how many additional write (or writev) system calls must be executed, and what processes make those system calls?