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sash



SYNOPSYS

       sash [-c command] [-f fileName ] [-p prompt] [-q] [-a]


DESCRIPTION

       The  sash  program  is a stand-alone shell which is useful
       for recovering from certain types of system failures.   In
       particular, it was created in order to cope with the prob­
       lem of missing shared libraries or important  executables.

       Sash  can  execute  external  programs,  as  in any shell.
       There are no restrictions on these commands, as the  stan­
       dard  shell  is used to execute them if there are any non-
       wildcard meta-characters in the command.

       More importantly, however, is that many  of  the  standard
       system commands are built-in to sash.  These built-in com­
       mands are:

            -ar, -chattr, -chgrp, -chmod, -chown, -cmp, -cp,
            -dd, -echo, -ed, -grep, -file, -find, -gunzip,
            -gzip, -kill, -ln, -ls, -lsattr, -mkdir, -mknod,
            -more, -mount, -mv, -printenv, -pwd, -rm, -rmdir,
            -sum, -sync, -tar, -touch, -umount, -where

       These commands are generally similar to the standard  pro­
       grams  with  similar names.  However, they are simpler and
       cruder than the external programs,  and  so  many  of  the
       options  are  not  implemented.  The restrictions for each
       built-in command are described later.

       The built-in commands which correspond  to  external  pro­
       grams  begin with a dash character in order to distinguish
       them from the external  programs.   So  typing  "ls",  for
       example,  will  attempt  to  run  the real ls program.  If
       "-ls" is typed, then the built-in command which mimics  ls
       is called.

       For the built-in commands, file names are expanded so that
       asterisks, question marks, and characters inside of square
       brackets  are  recognised and are expanded.  Arguments can
       be quoted using single quotes,  double  quotes,  or  back­
       slashes.   However,  no  other  command line processing is
       performed.  This includes specifying of file  redirection,
       and the specifying of a pipeline.

       If  an  external  program  is non-existant or fails to run
       correctly, then the "alias" built-in command may  be  used
       to  redefine the standard command so that it automatically
       runs the built-in command instead.  For example, the  com­
       mand  "alias  ls  -ls"  redefines "ls" to run the built-in
       command.  This saves you the pain of having to remember to
       type  the  leading dash all of the time.  If many external
              ments.   Arguments  containing  wildcards  can   be
              quoted  in order to defer their expansion until the
              alias is invoked.  If just name is  provided,  then
              the  definition  of  the specified command alias is
              displayed.  If nothing is provided, then the  defi­
              nitions of all aliases are displayed.

       aliasall
              This  defines  aliases for all of the built-in com­
              mands that start with dashes to  the  corresponding
              names  without the dashes.  This may be useful when
              the system is so corrupted that  no  external  pro­
              grams may be executed at all.

       -ar [txp][v] arfile [filename]...
              List  or  extract  files  from  an ar archive.  The
              arfile argument specifies a file  name  which  con­
              tains  the archive.  If no additional filenames are
              specified, then all files in the archive are  oper­
              ated  on.   Otherwise,  only  those archive members
              which have the same name as one of  the  additional
              filenames  are operated on.  Filenames which do not
              appear in the archive are ignored.  Archives cannot
              be  created  or  modified.   The archiver correctly
              handles 4.0BSD archives, and understands  both  the
              SysV  and  4.4BSD  extensions  for long file names.
              The extended pseudo-BSD formats are not  supported;
              nor are the two antediluvian binary formats derived
              from V7 and earlier.  (The  GNU  archiver  normally
              creates  archives  in  the  4.0BSD format with SysV
              extensions.)

       cd [dirName]
              If dirName is provided, then the current  directory
              is  changed  to the dirName.  If dirName is absent,
              then the current directory is changed to the user's
              home  directory  (value  of  the  $HOME environment
              variable).

       -chattr [+i] [-i] [+a] [-a] fileName ...
              Change the attributes of the specified files on  an
              ext2  or  ext3 file system.  Using a plus sign adds
              the specified attribute for  the  files.   Using  a
              minus sign removes the specified attributes for the
              files.  The 'i' attribute makes a file immutable so
              that it cannot be changed.  The 'a' attribute makes
              a file append-only.  This command is only available
              on Linux.

       -chgrp gid fileName ...
              Change  the  group  id  for  the  specified list of
              files.  The gid can either be a group  name,  or  a
              links to each other, are different sizes, differ at
              a particular byte number, or are identical.

       -cp srcName ... destName
              Copies  one  or  more files from the srcName to the
              destName.  If more than one srcName is given, or if
              destName  is a directory, then all the srcNames are
              copied into the destName directory  with  the  same
              names as the srcNames.

       -dd if=name of=name [bs=n] [count=n] [skip=n] [seek=n]
              Copy  data from one file to another with the speci­
              fied parameters.  The if and of arguments  must  be
              provided,  so stdin and stdout cannot be specified.
              The bs argument is the block size, and is a numeric
              value  (which defaults to 512 bytes).  Count is the
              number of blocks to be copied  (which  defaults  to
              end  of file for the input file).  Skip is the num­
              ber of blocks to ignore  before  copying  (seek  is
              used  if  possible, and the default is 0).  Seek is
              the number of blocks to seek  in  the  output  file
              before  writing  (and  defaults  to 0).  Any of the
              numeric decimal values can have one or more  trail­
              ing  letters  from  the set 'kbw', which multiplies
              the value by 1024, 512, and  2  respectively.   The
              command  reports the number of full blocks read and
              written, and whether or not any partial  block  was
              read or written.

       -echo [args] ...
              Echo the arguments to the -echo command.  Wildcards
              are expanded, so this is a convenient way to get  a
              quick  list of file names in a directory.  The out­
              put is always terminated with a newline.

       -ed [fileName]
              Edit the specified file using  line-mode  commands.
              The following ed commands are provided: = c r w i a
              d p l s f k z and q.   Line  numbers  can  be  con­
              stants,  ".", "$", "'x", /string/ and simple arith­
              metic combinations of these.  The  substitute  com­
              mand and the search expression can only use literal
              strings.  There are some small differences  in  the
              way that some commands behave.

       exec fileName [args]
              Execute  the  specified  program with the specified
              arguments.  This replaces sash  completely  by  the
              executed program.

       exit   Quit from sash.

              file names.  The -type option  specifies  that  the
              files  must have a type matching the specified list
              from the set: f d c b p s l.  These represent regu­
              lar  files,  directories,  character devices, block
              devices, named pipes, sockets, and symbolic  links.
              The  -size  option specifies that the files must be
              regular files or directories which contain at least
              the specified number of bytes.

       -grep [-in] word fileName ...
              Display  lines of the specified files which contain
              the given word.  If only one file  name  is  given,
              then  only the matching lines are printed.  If mul­
              tiple file names are given, then the file names are
              printed  along  with the matching lines.  Word must
              be a single word, (ie, not a  regular  expression).
              If -i is given, then case is ignored when doing the
              search.  If -n is given, then the line  numbers  of
              the matching lines are also printed.

       -gunzip inputFileName ... [-o outputPath]
              Uncompress  one  or  more  files that had been com­
              pressed using the gzip or compress algorithms.   If
              the  -o option is not given, then each of the input
              file names must have one of the  extensions  ".gz",
              ".tgz",  or  ".Z", and those files will be replaced
              by the uncompressed versions of those  files.   The
              original  files  will  be  deleted after the output
              files have been successfully created.   The  uncom­
              pressed  versions  of the files have the same names
              as the original file names,  except  for  a  simple
              modification  of their extensions.  If an extension
              is  ".tgz",  then  the  extension  is  replaced  by
              ".tar".   Otherwise, the ".gz" or ".Z" extension is
              removed.

              If the -o option is given,  then  the  input  files
              will  not be deleted, and the uncompressed versions
              of the files will be created as specified  by  out­
              putPath.   If  the output path is a directory, then
              the uncompressed versions of the input  files  will
              be  placed  in that directory with their file names
              modified as described above, or with the same  name
              if  the  input  file  name does not have one of the
              special extensions.  If the output path is a  regu­
              lar  file, then only one input file is allowed, and
              the uncompressed version of that input file is cre­
              ated  as  the output path exactly as specified.  If
              the output path is a  block  or  character  device,
              then  the  uncompressed versions of the input files
              are concatenated to the device.

              ".gz" extension is added.

              If  the  -o  option  is given, then the input files
              will not be deleted, and the compressed versions of
              the  files  will be created as specified by output­
              Path.  If the output path is a directory, then  the
              compressed  versions  of  the  input  files will be
              placed in that directory with their file names mod­
              ified  as  described  above.  If the output path is
              not a  directory,  then  only  one  input  file  is
              allowed,  and  the compressed version of that input
              file is created as the output path exactly as spec­
              ified.

              This command is only available if sash was compiled
              to use the gzip library.

       help [word]
              Displays a list of  built-in  commands  along  with
              their usage strings.  If a word is given, then just
              those commands whose name  or  usage  contains  the
              word  is  displayed.   If a word is specified which
              exactly matches a built-in  command  name,  then  a
              short  description  of the command and its usage is
              given.

       -kill [-signal] pid ...
              Sends the specified signal to the specified list of
              processes.   Signal  is  a numeric value, or one of
              the special values  HUP,  INT,  QUIT,  KILL,  TERM,
              STOP,  CONT,  USR1 or USR2.  If no signal is speci­
              fied then SIGTERM is used.

       -ln [-s] srcName ... destName
              Links one or more files from  the  srcName  to  the
              specified  destName.   If  there  are multiple src­
              Names, or destName is a directory, then the link is
              put in the destName directory with the same name as
              the source name.  The default links are hard links.
              Using -s makes symbolic links.  For symbolic links,
              only one srcName can be specified.

       -ls [-lidFC] fileName ...
              Display information about  the  specified  list  of
              file names.  The normal listing is simply a list of
              file names, one per line.   The  options  available
              are  -l,  -i, -d, and -F.  The -l option produces a
              long listing giving the  normal  'ls'  information.
              The  -i  option  displays  the inode numbers of the
              files.  The -d option displays information about  a
              directory,  instead of the files within it.  The -F
              option appends a slash or asterisk to the file name
              Creates  the  specified directories.  They are cre­
              ated with the default permissions.

       -mknod fileName type major minor
              Creates a special device node, either  a  character
              file  or a block file.  Filename is the name of the
              node.  Type is either 'c' or  'd'.   Major  is  the
              major  device  number.   Minor  is the minor device
              number.  Both of these numbers are decimal.

       -more fileName ...
              Type out the contents of the specified file  names,
              one  page  at a time.  For each page displayed, you
              can type 'n' and a return to go to the  next  file,
              'q' and a return to quit the command completely, or
              just a return to go to the next page.  The environ­
              ment  variables  LINES  and COLS can be used to set
              the page size.

       -mount [-t type] [-r] [-s] [-e] [-m] devName dirName
              Mount a filesystem on a  directory  name.   The  -t
              option  specifies  the  type  of  filesystem  being
              mounted, and defaults to "ext3" for Linux and "ffs"
              for  BSD.   The  -r  option  indicates to mount the
              filesystem read-only.  The -s option  indicates  to
              mount  the filesystem no-suid.  The -e option indi­
              cates to mount  the  filesystem  no-exec.   The  -m
              option  indicates  to  remount  an  already mounted
              filesystem.  The -m option  is  only  available  on
              Linux.

       -mv srcName ... destName
              Moves  one  or  more  files from the srcName to the
              destName.  If multiple srcNames are  given,  or  if
              destName  is  a  directory,  then  the srcNames are
              copied into the destination directory with the same
              names  as  the  srcNames.   Renames  are  attempted
              first, but if this fails because of the files being
              on  different  filesystems, then copies and deletes
              are done instead.

       -printenv [name]
              If name is not given, this prints out the values of
              all  the current environment variables.  If name is
              given, then only that environment variable value is
              printed.

       prompt [word] ...
              Sets  the  prompt  string  that is displayed before
              reading of a command.  A space is always  added  to
              the specified prompt.

       source fileName
              Execute commands which are contained in the  speci­
              fied file name.

       -sum fileName ...
              Calculates  checksums  for one or more files.  This
              is the 16 bit checksum compatible with the BSD  sum
              program.

       -sync  Do  a  "sync" system call to force dirty blocks out
              to the disk.

       -tar [ctxv]f tarFileName [fileName] ...
              Create, list or extract files from a  tar  archive.
              The  f  option  must  be  specified,  and accepts a
              device or file name argument which contains the tar
              archive.   When  creating,  at  least one file name
              must be specified to be stored.  If a file name  is
              a  directory,  then  all  the files and directories
              within the directory are stored.  Linked files  and
              other  special file types are not handled properly.
              When listing or extracting files, only those  files
              starting  with  the  specified  file names are pro­
              cessed.  If no file names are specified,  then  all
              files   in  the  archive  are  processed.   Leading
              slashes in the tar archive file  names  are  always
              removed  so  that  you  might  need to cd to "/" to
              restore files which had absolute paths.

       -touch fileName ...
              Updates the modify times of the specifed files.  If
              a file does not exist, then it will be created with
              the default protection.

       umask [mask]
              If mask is given, sets the "umask" value  used  for
              initializing   the  permissions  of  newly  created
              files.  If mask is  not  given,  then  the  current
              umask  value  is  printed.   The  mask  is an octal
              value.

       -umount [-f] fileName
              Unmounts a file system.  The file name  can  either
              be  the  device  name which is mounted, or else the
              directory name which the  file  system  is  mounted
              onto.   The  -f option unmounts the filesystem even
              if it is being used.  The -f option is only  avail­
              able on BSD.

       unalias name
              Remove the definition for the specified alias.

       name specified by the next argument, and then exits.  This
       feature can be used to create executable scripts for  sash
       by starting the script file with a line similar to:
            #! /bin/sash -f

       The -p option takes the next argument as the prompt string
       to be used when prompting for commands.

       The -q option makes sash quiet, which simply means that it
       doesn't  print its introduction line when it starts.  This
       option is also implied if the -c or -f options are used.

       The -a option creates aliases for the built-in commands so
       that  they  replace  the  corresponding standard commands.
       This is the same result as if the 'aliasall'  command  was
       used.


SYSTEM RECOVERY

       This  section contains some useful information about using
       sash with lilo to perform system recovery in  some  situa­
       tions.  Similar concepts should exist for other boot load­
       ers and operating systems.

       When important shared libraries  are  being  upgraded,  it
       might  be  a  good  idea to have sash already running on a
       console by itself.  Then if there is a  problem  with  the
       shared  libraries  sash  will be unaffected and you may be
       able to use it to fix the problem.

       If a problem with the system shows up at boot time so that
       you  cannot enter multi-user mode and log in, then you can
       first try booting into single-user mode by adding the sin­
       gle  keyword  after  your  kernel  image  name at the lilo
       prompt.  If you manage to reach a shell prompt,  then  you
       can  run  sash from that shell (if necessary).  One reason
       for doing this is that you might need to  use  the  -mount
       command with the -m option to remount the root file system
       so that it can be modified.

       If you cannot reach the shell in  single-user  mode,  then
       you can try running sash directly as a replacement for the
       init process.  This is done by adding  the  init=/bin/sash
       keyword  after  your kernel image name at the lilo prompt.
       When this is done, then the use of  the  aliasall  command
       might be useful to reduce attempts to access the root file
       system when running commands.

       If your root file system is so corrupted that  you  cannot
       get  sash to run at all, then you will have to resort to a
       system recovery floppy.


WARNINGS


  




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