| 1 | |
| 2 |
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| 3 | ====================
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| 4 | kAFS: AFS FILESYSTEM
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| 5 | ====================
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| 6 |
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| 7 | |
| 8 |
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| 9 | - Overview.
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| 10 | - Usage.
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| 11 | - Mountpoints.
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| 12 | - Dynamic root.
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| 13 | - Proc filesystem.
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| 14 | - The cell database.
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| 15 | - Security.
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| 16 | - The @sys substitution.
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| 17 |
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| 18 |
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| 19 | Overview
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| 20 | ========
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| 21 |
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| 22 | This filesystem provides a fairly simple secure AFS filesystem driver. It is
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| 23 | under development and does not yet provide the full feature set. The features
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| 24 | it does support include:
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| 25 |
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| 26 | (*) Security (currently only AFS kaserver and KerberosIV tickets).
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| 27 |
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| 28 | (*) File reading and writing.
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| 29 |
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| 30 | (*) Automounting.
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| 31 |
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| 32 | (*) Local caching (via fscache).
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| 33 |
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| 34 | It does not yet support the following AFS features:
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| 35 |
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| 36 | (*) pioctl() system call.
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| 37 |
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| 38 |
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| 39 | Compilation
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| 40 | ===========
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| 41 |
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| 42 | The filesystem should be enabled by turning on the kernel configuration
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| 43 | options::
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| 44 |
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| 45 | CONFIG_AF_RXRPC - The RxRPC protocol transport
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| 46 | CONFIG_RXKAD - The RxRPC Kerberos security handler
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| 47 | CONFIG_AFS_FS - The AFS filesystem
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| 48 |
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| 49 | Additionally, the following can be turned on to aid debugging::
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| 50 |
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| 51 | CONFIG_AF_RXRPC_DEBUG - Permit AF_RXRPC debugging to be enabled
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| 52 | CONFIG_AFS_DEBUG - Permit AFS debugging to be enabled
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| 53 |
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| 54 | They permit the debugging messages to be turned on dynamically by manipulating
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| 55 | the masks in the following files::
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| 56 |
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| 57 | /sys/module/af_rxrpc/parameters/debug
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| 58 | /sys/module/kafs/parameters/debug
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| 59 |
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| 60 |
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| 61 | Usage
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| 62 | =====
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| 63 |
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| 64 | When inserting the driver modules the root cell must be specified along with a
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| 65 | list of volume location server IP addresses::
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| 66 |
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| 67 | modprobe rxrpc
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| 68 | modprobe kafs rootcell=cambridge.redhat.com:172.16.18.73:172.16.18.91
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| 69 |
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| 70 | The first module is the AF_RXRPC network protocol driver. This provides the
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| 71 | RxRPC remote operation protocol and may also be accessed from userspace. See:
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| 72 |
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| 73 | Documentation/networking/rxrpc.rst
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| 74 |
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| 75 | The second module is the kerberos RxRPC security driver, and the third module
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| 76 | is the actual filesystem driver for the AFS filesystem.
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| 77 |
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| 78 | Once the module has been loaded, more modules can be added by the following
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| 79 | procedure::
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| 80 |
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| 81 | echo add grand.central.org 18.9.48.14:128.2.203.61:130.237.48.87 >/proc/fs/afs/cells
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| 82 |
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| 83 | Where the parameters to the "add" command are the name of a cell and a list of
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| 84 | volume location servers within that cell, with the latter separated by colons.
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| 85 |
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| 86 | Filesystems can be mounted anywhere by commands similar to the following::
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| 87 |
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| 88 | mount -t afs "%cambridge.redhat.com:root.afs." /afs
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| 89 | mount -t afs "#cambridge.redhat.com:root.cell." /afs/cambridge
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| 90 | mount -t afs "#root.afs." /afs
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| 91 | mount -t afs "#root.cell." /afs/cambridge
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| 92 |
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| 93 | Where the initial character is either a hash or a percent symbol depending on
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| 94 | whether you definitely want a R/W volume (percent) or whether you'd prefer a
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| 95 | R/O volume, but are willing to use a R/W volume instead (hash).
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| 96 |
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| 97 | The name of the volume can be suffixes with ".backup" or ".readonly" to
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| 98 | specify connection to only volumes of those types.
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| 99 |
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| 100 | The name of the cell is optional, and if not given during a mount, then the
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| 101 | named volume will be looked up in the cell specified during modprobe.
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| 102 |
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| 103 | Additional cells can be added through /proc (see later section).
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| 104 |
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| 105 |
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| 106 | Mountpoints
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| 107 | ===========
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| 108 |
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| 109 | AFS has a concept of mountpoints. In AFS terms, these are specially formatted
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| 110 | symbolic links (of the same form as the "device name" passed to mount). kAFS
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| 111 | presents these to the user as directories that have a follow-link capability
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| 112 | (i.e.: symbolic link semantics). If anyone attempts to access them, they will
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| 113 | automatically cause the target volume to be mounted (if possible) on that site.
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| 114 |
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| 115 | Automatically mounted filesystems will be automatically unmounted approximately
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| 116 | twenty minutes after they were last used. Alternatively they can be unmounted
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| 117 | directly with the umount() system call.
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| 118 |
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| 119 | Manually unmounting an AFS volume will cause any idle submounts upon it to be
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| 120 | culled first. If all are culled, then the requested volume will also be
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| 121 | unmounted, otherwise error EBUSY will be returned.
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| 122 |
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| 123 | This can be used by the administrator to attempt to unmount the whole AFS tree
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| 124 | mounted on /afs in one go by doing::
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| 125 |
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| 126 | umount /afs
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| 127 |
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| 128 |
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| 129 | Dynamic Root
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| 130 | ============
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| 131 |
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| 132 | A mount option is available to create a serverless mount that is only usable
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| 133 | for dynamic lookup. Creating such a mount can be done by, for example::
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| 134 |
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| 135 | mount -t afs none /afs -o dyn
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| 136 |
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| 137 | This creates a mount that just has an empty directory at the root. Attempting
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| 138 | to look up a name in this directory will cause a mountpoint to be created that
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| 139 | looks up a cell of the same name, for example::
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| 140 |
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| 141 | ls /afs/grand.central.org/
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| 142 |
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| 143 |
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| 144 | Proc Filesystem
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| 145 | ===============
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| 146 |
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| 147 | The AFS module creates a "/proc/fs/afs/" directory and populates it:
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| 148 |
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| 149 | (*) A "cells" file that lists cells currently known to the afs module and
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| 150 | their usage counts::
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| 151 |
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| 152 | [root@andromeda ~]# cat /proc/fs/afs/cells
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| 153 | USE NAME
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| 154 | 3 cambridge.redhat.com
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| 155 |
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| 156 | (*) A directory per cell that contains files that list volume location
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| 157 | servers, volumes, and active servers known within that cell::
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| 158 |
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| 159 | [root@andromeda ~]# cat /proc/fs/afs/cambridge.redhat.com/servers
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| 160 | USE ADDR STATE
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| 161 | 4 172.16.18.91 0
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| 162 | [root@andromeda ~]# cat /proc/fs/afs/cambridge.redhat.com/vlservers
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| 163 | ADDRESS
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| 164 | 172.16.18.91
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| 165 | [root@andromeda ~]# cat /proc/fs/afs/cambridge.redhat.com/volumes
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| 166 | USE STT VLID[0] VLID[1] VLID[2] NAME
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| 167 | 1 Val 20000000 20000001 20000002 root.afs
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| 168 |
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| 169 |
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| 170 | The Cell Database
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| 171 | =================
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| 172 |
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| 173 | The filesystem maintains an internal database of all the cells it knows and the
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| 174 | IP addresses of the volume location servers for those cells. The cell to which
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| 175 | the system belongs is added to the database when modprobe is performed by the
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| 176 | "rootcell=" argument or, if compiled in, using a "kafs.rootcell=" argument on
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| 177 | the kernel command line.
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| 178 |
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| 179 | Further cells can be added by commands similar to the following::
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| 180 |
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| 181 | echo add CELLNAME VLADDR[:VLADDR][:VLADDR]... >/proc/fs/afs/cells
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| 182 | echo add grand.central.org 18.9.48.14:128.2.203.61:130.237.48.87 >/proc/fs/afs/cells
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| 183 |
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| 184 | No other cell database operations are available at this time.
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| 185 |
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| 186 |
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| 187 | Security
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| 188 | ========
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| 189 |
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| 190 | Secure operations are initiated by acquiring a key using the klog program. A
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| 191 | very primitive klog program is available at:
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| 192 |
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| 193 | https://people.redhat.com/~dhowells/rxrpc/klog.c
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| 194 |
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| 195 | This should be compiled by::
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| 196 |
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| 197 | make klog LDLIBS="-lcrypto -lcrypt -lkrb4 -lkeyutils"
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| 198 |
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| 199 | And then run as::
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| 200 |
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| 201 | ./klog
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| 202 |
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| 203 | Assuming it's successful, this adds a key of type RxRPC, named for the service
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| 204 | and cell, e.g.: "afs@<cellname>". This can be viewed with the keyctl program or
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| 205 | by cat'ing /proc/keys::
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| 206 |
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| 207 | [root@andromeda ~]# keyctl show
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| 208 | Session Keyring
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| 209 | -3 --alswrv 0 0 keyring: _ses.3268
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| 210 | 2 --alswrv 0 0 \_ keyring: _uid.0
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| 211 | 111416553 --als--v 0 0 \_ rxrpc: [email protected]
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| 212 |
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| 213 | Currently the username, realm, password and proposed ticket lifetime are
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| 214 | compiled into the program.
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| 215 |
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| 216 | It is not required to acquire a key before using AFS facilities, but if one is
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| 217 | not acquired then all operations will be governed by the anonymous user parts
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| 218 | of the ACLs.
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| 219 |
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| 220 | If a key is acquired, then all AFS operations, including mounts and automounts,
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| 221 | made by a possessor of that key will be secured with that key.
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| 222 |
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| 223 | If a file is opened with a particular key and then the file descriptor is
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| 224 | passed to a process that doesn't have that key (perhaps over an AF_UNIX
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| 225 | socket), then the operations on the file will be made with key that was used to
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| 226 | open the file.
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| 227 |
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| 228 |
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| 229 | The @sys Substitution
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| 230 | =====================
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| 231 |
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| 232 | The list of up to 16 @sys substitutions for the current network namespace can
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| 233 | be configured by writing a list to /proc/fs/afs/sysname::
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| 234 |
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| 235 | [root@andromeda ~]# echo foo amd64_linux_26 >/proc/fs/afs/sysname
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| 236 |
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| 237 | or cleared entirely by writing an empty list::
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| 238 |
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| 239 | [root@andromeda ~]# echo >/proc/fs/afs/sysname
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| 240 |
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| 241 | The current list for current network namespace can be retrieved by::
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| 242 |
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| 243 | [root@andromeda ~]# cat /proc/fs/afs/sysname
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| 244 | foo
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| 245 | amd64_linux_26
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| 246 |
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| 247 | When @sys is being substituted for, each element of the list is tried in the
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| 248 | order given.
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| 249 |
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| 250 | By default, the list will contain one item that conforms to the pattern
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| 251 | "<arch>_linux_26", amd64 being the name for x86_64.
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