Unix (all-caps UNIX for the trademark) is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, developed in the 1970s at the Bell Labs research center by Ken Thompson, Dennis Ritchie, and others.

Rbcafe » Unix



base64 – Encoding “base64”


package require Tcl 8.2
package require Trf 2.1p2
base64 options… data


The command base64 is one of several data encodings provided by the
package trf. See trf-intro for an overview of the whole package.

This encoding transforms every block of three bytes into a block of
four bytes, each of which is printable, i.e. 7bit ASCII. This implies
that the result is valid UTF-8 too. The command uses essentially the
same algorithm as for uuencode, except for a different mapping from
6-bit fragments to printable bytes.

base64 options… data

-mode encode|decode

This option has to be present and is always understood by
the encoding.

For immediate mode the argument value specifies the oper-
ation to use. For an attached encoding it specifies the
operation to use for writing. Reading will automatically
use the reverse operation. See section IMMEDIATE versus
ATTACHED for explanations of these two terms.

Beyond the argument values listed above all unique abbre-
viations are recognized too.

Encode converts from arbitrary (most likely binary) data
into the described representation, decode does the
reverse .

-attach channel

The presence/absence of this option determines the main
operation mode of the transformation.

If present the transformation will be stacked onto the
channel whose handle was given to the option and run in
attached mode. More about this in section IMMEDIATE ver-

If the option is absent the transformation is used in
immediate mode and the options listed below are recog-
nized. More about this in section IMMEDIATE versus

-in channel

This options is legal if and only if the transformation
is used in immediate mode. It provides the handle of the
channel the data to transform has to be read from.

If the transformation is in immediate mode and this
option is absent the data to transform is expected as the
last argument to the transformation.

-out channel

This options is legal if and only if the transformation
is used in immediate mode. It provides the handle of the
channel the generated transformation result is written

If the transformation is in immediate mode and this
option is absent the generated data is returned as the
result of the command itself.


[1] The encoding is equivalent to PGP’s ASCII armor and was also
accepted as one of the MIME encodings for encapsulation of
binary data. See RFC 2045
tor.org/rfc/rfc2045.txt) for details and the specification of
this encoding.

[2] The encoding buffers 2 bytes.


The transformation distinguishes between two main ways of using it.
These are the immediate and attached operation modes.

For the attached mode the option -attach is used to associate the
transformation with an existing channel. During the execution of the
command no transformation is performed, instead the channel is changed
in such a way, that from then on all data written to or read from it
passes through the transformation and is modified by it according to
the definition above. This attachment can be revoked by executing the
command unstack for the chosen channel. This is the only way to do this
at the Tcl level.

In the second mode, which can be detected by the absence of option
-attach, the transformation immediately takes data from either its com-
mandline or a channel, transforms it, and returns the result either as
result of the command, or writes it into a channel. The mode is named
after the immediate nature of its execution.

Where the data is taken from, and delivered to, is governed by the
presence and absence of the options -in and -out. It should be noted
that this ability to immediately read from and/or write to a channel is
an historic artifact which was introduced at the beginning of Trf’s
life when Tcl version 7.6 was current as this and earlier versions have
trouble to deal with \0 characters embedded into either input or out-


Rbcafe » Unix



automount — automatic server mount / unmount daemon


automount [-V] [-d] [-D type] [-1] [-tm secs] [-tl secs] [-s] [-tcp]
[-m directory map -mnt directory] …


automount is a daemon that automatically mounts network filesystems when
they are first accessed and later unmounts them when they are idle.

automount creates a virtual filesystem mounted at one or more places in
the client’s file and directory hierarchy. Potential server mount points
within this virtual filesystem appear as symbolic links. Reading a sym-
bolic link causes automount to mount the associated remote filesystem in
a separate hierarchy and to return the path to the real mount point as
the target of the symlink.

To make the “trigger” symbolic links used by automount distinguishable
from normal symbolic links, the sticky bit is set in the mode flags for
the link. Programs which would normally traverse symbolic links can test
for this bit and avoid triggering the mount. Various parts of the sys-
tem, including ls(1), have been modified in this way.

Each virtual filesystem created by automount is governed by a correspond-
ing map. One or more maps and the location in the hierarchy where they
are to appear may be specified on the command line with -m and -mnt:

-m directory map

is followed by a specification of the private mount directory where the
actual mounts are to be established:

-mnt actual_root

Each map’s hierarchy is rooted at the directory specified.


A map may be file or a special map. A file map is a file containing a
list of entries of the form:

location mount_options server:path

mount_options must be a comma-separated list of options drawn from the
options known to mount(8) and mount_nfs(8). automount will automatically
make available at the map’s mount point the directory specified by
server:path (as a symlink). When the symlink is traversed, it will mount
the server in the directory specified with -mnt and return the real mount
point as the result of the symlink resolution.


In addition to reading files specifying mount maps, automount supports
the “-fstab”, “-static”, and “-nsl” maps. The “-fstab” and
“-static” maps are derived from fstab(5) data (as provided by

All mounts in fstab(5) without the “net” option will be made to appear
at the fstab(5)-specified location in the form of a symlink into the
directory where the “-static” map is actually mounted (itself a direc-
tory of symlinks). For example, the entry:

server:/Network/Applications /Network/Applications nfs nosuid 0 0

and automount invocation

automount -m /automount/static -static -mnt /private/var/automount

result in a non-trigger symlink /Network/Applications pointing to /auto-
mount/static/Network/Applications which, when traversed, causes
server:/Network/Applications to be mounted on /private/var/automount/Net-
work/Applications (which would then be returned from reading the link).

All mounts with the “net” option will be mounted within the “-fstab”
map’s filesystem using a path of the form:


For such mounts, the path specified in the fstab(5) entry will be
ignored. For example, if the fstab(5) database contained an entry for


and automount was started as follows:

automount -m /Useful -fstab -mnt /private/Useful

then a symlink would appear in /Useful, /Useful/polaris/Library/Fonts,
and link to /private/Useful/polaris/Library/Fonts where the filesystem is
actually mounted when the symlink is traversed.

The “-nsl” map generates its filesystem hierarchy from information gen-
erated by NSL. NSL “neighborhoods” are presented as directories, popu-
lated by server entries.

Accessing servers in the NSL hierarchy may prompt the user for authenti-


-V Print version and host information, then quit

-m directory map
Associate the specified map with the given directory. The direc-
tory will be created if it doesn’t exist. map may be the name of
a file, or it may be the name of a special map. See the FILE
MAPS and SPECIAL MAPS sections above.

-d Run automount in debug mode. The program remains in the fore-
ground and sends debugging information to standard output.

-D type
Log debug messages for type. type may be “mount”, “proc”,
“mount”, “select”, “options”, “nsl”, or “all”. Multiple -D
options may be specified.

-1 (The numeric digit “one”.) Modifies the “-fstab” and
“-static” maps to do mounts “one at a time”, when an actual
mount point is traversed rather than mounting all mounts from a
given server when the first of its mounts is referenced and

-tm secs
Set the timeout for NFS mounts to secs seconds. The default
value is 20 seconds. The “mnttimeo=n” mount option overrides
this default.

-tl secs
Set the time-to-live for NFS mounts to secs seconds. The default
value is 3600 seconds. The “ttl=n” mount option overrides this

automount periodically checks all its mounted filesystems. If it
finds any filesystems that have been idle for their associated
time-to-live value, it will attempt to unmount them. An unmount
will only be successful if there are no processes with open files
in that filesystem. Unless -1 is specified, if one or more
mounts from a given server are found to be active, any mounts
from that server that were successfully unmounted will be immea-
diately remounted.

Supplying a ttl value of 0 will disable this behavior and allow
servers to remain mounted forever.

-s Force all mounts at startup and never expire any mounts.

-tcp Mount servers using TCP if possible, otherwise using UDP (the
default is to try UDP first, then TCP). Per mount_nfs(8), “-T”,
“TCP”, or “tcp” mount options have the same effect as specifying
-tcp; “-U”, “UDP”, or “udp” mount options force the default
behavior of trying UDP first even if -tcp is specified.


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