NamespaceWhat it isolatesWhat the process seesPIDProcess IDsOwn process tree, starts at PID 1MountFilesystem mount pointsOwn mount table, can have different rootNetworkNetwork interfaces, routingOwn interfaces, IP addresses, portsUserUID/GID mappingCan be root inside, nobody outsideUTSHostnameOwn hostnameIPCSysV IPC, POSIX message queuesOwn shared memory, semaphoresCgroupCgroup root directoryOwn cgroup hierarchyTimeSystem clocks (monotonic, boot)Own system uptime and clock offsetsNamespaces are what Docker containers use. When you run a container, it gets its own PID namespace (cannot see host processes), its own mount namespace (own filesystem view), its own network namespace (own interfaces), and so on.
然而，穿透这些变化的表象，其底层贯穿着一条坚韧的“不变”主线：作为连接亿万消费者与海量供给端的枢纽，平台的根本价值始终在于解决信息不对称、提升产业效率。
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Photographer: Yuki Iwamura/Bloomberg。业内人士推荐safew官方下载作为进阶阅读
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The 386 supports four privilege rings (0 through 3), though in practice nearly all operating systems use just two: ring 0 for the kernel and ring 3 for user programs. Three privilege levels interact on every segment access: CPL (Current Privilege Level), DPL (Descriptor Privilege Level), and RPL (Requested Privilege Level).