请帮忙。我刚买了这个 VPS，在上面安装了 Ubuntu-16。以root用户身份登录并发出apt-get update。我收到以下错误。可能出了什么问题。
错误日志
: Read-only file system)
W: Problem unlinking the file /var/lib/apt/lists/partial/us.archive.ubuntu.com_ubuntu_dists_xenial-updates_universe_binary-amd64_Packages - TransactionAbort (30: Read-only file system)
W: Problem unlinking the file /var/lib/apt/lists/partial/us.archive.ubuntu.com_ubuntu_dists_xenial-updates_universe_binary-i386_Packages - TransactionAbort (30: Read-only file system)
W: Problem unlinking the file /var/lib/apt/lists/partial/us.archive.ubuntu.com_ubuntu_dists_xenial-updates_universe_i18n_Translation-en - TransactionAbort (30: Read-only file system)
W: Problem unlinking the file /var/lib/apt/lists/partial/us.archive.ubuntu.com_ubuntu_dists_xenial-updates_multiverse_binary-amd64_Packages - TransactionAbort (30: Read-only file system)
W: Problem unlinking the file /var/lib/apt/lists/partial/us.archive.ubuntu.com_ubuntu_dists_xenial-updates_multiverse_binary-i386_Packages - TransactionAbort (30: Read-only file system)
W: Problem unlinking the file /var/lib/apt/lists/partial/us.archive.ubuntu.com_ubuntu_dists_xenial-updates_multiverse_i18n_Translation-en - TransactionAbort (30: Read-only file system)
W: Problem unlinking the file /var/lib/apt/lists/partial/us.archive.ubuntu.com_ubuntu_dists_xenial-updates_main_binary-i386_Packages - PrepareFiles (30: Read-only file system)
W: Problem unlinking the file /var/lib/apt/lists/partial/us.archive.ubuntu.com_ubuntu_dists_xenial-updates_main_i18n_Translation-en - PrepareFiles (30: Read-only file system)
W: Problem unlinking the file /var/lib/apt/lists/partial/us.archive.ubuntu.com_ubuntu_dists_xenial-updates_restricted_binary-amd64_Packages - PrepareFiles (30: Read-only file system)
W: Problem unlinking the file /var/lib/apt/lists/partial/us.archive.ubuntu.com_ubuntu_dists_xenial-updates_restricted_binary-i386_Packages - PrepareFiles (30: Read-only file system)
W: Problem unlinking the file /var/lib/apt/lists/partial/us.archive.ubuntu.com_ubuntu_dists_xenial-updates_restricted_i18n_Translation-en - PrepareFiles (30: Read-only file system)
W: Problem unlinking the file /var/lib/apt/lists/partial/us.archive.ubuntu.com_ubuntu_dists_xenial-updates_universe_binary-amd64_Packages - PrepareFiles (30: Read-only file system)
W: Problem unlinking the file /var/lib/apt/lists/partial/us.archive.ubuntu.com_ubuntu_dists_xenial-updates_universe_binary-i386_Packages - PrepareFiles (30: Read-only file system)
W: Problem unlinking the file /var/lib/apt/lists/partial/us.archive.ubuntu.com_ubuntu_dists_xenial-updates_universe_i18n_Translation-en - PrepareFiles (30: Read-only file system)
W: Problem unlinking the file /var/lib/apt/lists/partial/us.archive.ubuntu.com_ubuntu_dists_xenial-updates_multiverse_binary-amd64_Packages - PrepareFiles (30: Read-only file system)
W: Problem unlinking the file /var/lib/apt/lists/partial/us.archive.ubuntu.com_ubuntu_dists_xenial-updates_multiverse_binary-i386_Packages - PrepareFiles (30: Read-only file system)
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/xenial/InRelease Could not execute 'apt-key' to verify signature (is gnupg installed?)
E: Failed to fetch http://security.ubuntu.com/ubuntu/dists/xenial-security/main/binary-amd64/Packages Could not open file /var/lib/apt/lists/partial/security.ubuntu.com_ubuntu_dists_xenial-security_main_binary-amd64_Packages.xz - open (30: Read-only file system) [IP: 2001:67c:1560:8001::11 80]
E: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/xenial-backports/restricted/binary-amd64/Packages Could not open file /var/lib/apt/lists/partial/us.archive.ubuntu.com_ubuntu_dists_xenial-backports_restricted_binary-amd64_Packages.xz - open (30: Read-only file system) [IP: 2001:67c:1562::16 80]
E: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/xenial-updates/main/binary-amd64/Packages Could not open file /var/lib/apt/lists/partial/us.archive.ubuntu.com_ubuntu_dists_xenial-updates_main_binary-amd64_Packages.xz - open (30: Read-only file system) [IP: 91.189.91.26 80]
W: Some index files failed to download. They have been ignored, or old ones used instead.
W: Problem unlinking the file /var/cache/apt/pkgcache.bin - RemoveCaches (30: Read-only file system)
W: Problem unlinking the file /var/cache/apt/srcpkgcache.bin - RemoveCaches (30: Read-only file system)
W: Not using locking for read only lock file /var/lib/dpkg/lock
root@localhost:~#
root@localhost:~# apt-get update
W: chown to _apt:root of directory /var/lib/apt/lists/partial failed - SetupAPTPartialDirectory (30: Read-only file system)
W: chmod 0700 of directory /var/lib/apt/lists/partial failed - SetupAPTPartialDirectory (30: Read-only file system)
W: Not using locking for read only lock file /var/lib/apt/lists/lock
W: Problem unlinking the file /var/lib/apt/lists/partial/.apt-acquire-privs-test.YsPtbN - IsAccessibleBySandboxUser (30: Read-only file system)
W: Problem unlinking the file /var/lib/apt/lists/partial/.apt-acquire-privs-test.OMQwro - IsAccessibleBySandboxUser (30: Read-only file system)
W: Problem unlinking the file /var/lib/apt/lists/partial/.apt-acquire-privs-test.ub0zHZ - IsAccessibleBySandboxUser (30: Read-only file system)
W: Problem unlinking the file /var/lib/apt/lists/partial/.apt-acquire-privs-test.ysgDXA - IsAccessibleBySandboxUser (30: Read-only file system)
W: Problem unlinking the file /var/lib/apt/lists/partial/security.ubuntu.com_ubuntu_dists_xenial-security_InRelease - PrepareFiles (30: Read-only file system)
W: Problem unlinking the file /var/lib/apt/lists/partial/security.ubuntu.com_ubuntu_dists_xenial-security_Release - PrepareFiles (30: Read-only file system)
W: The repository 'http://security.ubuntu.com/ubuntu xenial-security Release' does not have a Release file.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.
W: Problem unlinking the file /var/lib/apt/lists/partial/security.ubuntu.com_ubuntu_dists_xenial-security_main_binary-amd64_Packages.diff_Index - PrepareFiles (30: Read-only file system)
W: Problem unlinking the file /var/lib/apt/lists/partial/security.ubuntu.com_ubuntu_dists_xenial-security_main_binary-i386_Packages.diff_Index - PrepareFiles (30: Read-only file system)
W: Problem unlinking the file /var/lib/apt/lists/partial/us.archive.ubuntu.com_ubuntu_dists_xenial-updates_multiverse_binary-i386_Packages - PrepareFiles (30: Read-only file system)
W: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/xenial/InRelease Could not execute 'apt-key' to verify signature (is gnupg installed?)
E: Failed to fetch http://security.ubuntu.com/ubuntu/dists/xenial-security/main/binary-amd64/Packages Could not open file /var/lib/apt/lists/partial/security.ubuntu.com_ubuntu_dists_xenial-security_main_binary-amd64_Packages.xz - open (30: Read-only file system) [IP: 2001:67c:1560:8001::11 80]
E: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/xenial-backports/restricted/binary-amd64/Packages Could not open file /var/lib/apt/lists/partial/us.archive.ubuntu.com_ubuntu_dists_xenial-backports_restricted_binary-amd64_Packages.xz - open (30: Read-only file system) [IP: 2001:67c:1562::16 80]
E: Failed to fetch http://us.archive.ubuntu.com/ubuntu/dists/xenial-updates/main/binary-amd64/Packages Could not open file /var/lib/apt/lists/partial/us.archive.ubuntu.com_ubuntu_dists_xenial-updates_main_binary-amd64_Packages.xz - open (30: Read-only file system) [IP: 91.189.91.26 80]
W: Some index files failed to download. They have been ignored, or old ones used instead.
W: Problem unlinking the file /var/cache/apt/pkgcache.bin - RemoveCaches (30: Read-only file system)
W: Problem unlinking the file /var/cache/apt/srcpkgcache.bin - RemoveCaches (30: Read-only file system)
W: Not using locking for read only lock file /var/lib/dpkg/lock
root@localhost:~#