How do I use the nohup command without getting nohup out

Question

I have a problem with the nohup command   When I run my job  I have a lot of data  The output nohup out becomes too large and my process slows down  How can I run this command without getting nohup out

User · Answer

nohup some command  gt   dev null 2 gt  amp 1 amp    That s all you need to do

User · Answer

Following command will let you run something in the background without getting nohup out   nohup command  tee  amp    In this way  you will be able to get console output while running script on the remote server

User · Answer

The nohup command only writes to nohup out if the output would otherwise go to the terminal  If you have redirected the output of the command somewhere else - including  dev null - that s where it goes instead    nohup command  gt  dev null 2 gt  amp 1     doesn t create nohup out   If you re using nohup  that probably means you want to run the command in the background by putting another  amp  on the end of the whole thing    nohup command  gt  dev null 2 gt  amp 1  amp    runs in background  still doesn t create nohup out   On Linux  running a job with nohup automatically closes its input as well   On other systems  notably BSD and macOS  that is not the case  so when running in the background  you might want to close input manually  While closing input has no effect on the creation or not of nohup out  it avoids another problem  if a background process tries to read anything from standard input  it will pause  waiting for you to bring it back to the foreground and type something  So the extra-safe version looks like this   nohup command  lt  dev null  gt  dev null 2 gt  amp 1  amp    completely detached from terminal    Note  however  that this does not prevent the command from accessing the terminal directly  nor does it remove it from your shell s process group  If you want to do the latter  and you are running bash  ksh  or zsh  you can do so by running disown with no argument as the next command  That will mean the background process is no longer associated with a shell  job  and will not have any signals forwarded to it from the shell   Note the distinction  a disowned process gets no signals forwarded to it automatically by its parent shell - but without nohup  it will still receive a HUP signal sent via other means  such as a manual kill command   A nohup ed process ignores any and all HUP signals  no matter how they are sent    Explanation   In Unixy systems  every source of input or target of output has a number associated with it called a  file descriptor   or  fd  for short  Every running program   process   has its own set of these  and when a new process starts up it has three of them already open   standard input   which is fd 0  is open for the process to read from  while  standard output   fd 1  and  standard error   fd 2  are open for it to write to  If you just run a command in a terminal window  then by default  anything you type goes to its standard input  while both its standard output and standard error get sent to that window   But you can ask the shell to change where any or all of those file descriptors point before launching the command  that s what the redirection   lt    lt  lt    gt    gt  gt   and pipe     operators do   The pipe is the simplest of these    command1   command2 arranges for the standard output of command1 to feed directly into the standard input of command2   This is a very handy arrangement that has led to a particular design pattern in UNIX tools  and explains the existence of standard error  which allows a program to send messages to the user even though its output is going into the next program in the pipeline   But you can only pipe standard output to standard input  you can t send any other file descriptors to a pipe without some juggling   The redirection operators are friendlier in that they let you specify which file descriptor to redirect   So 0 lt infile reads standard input from the file named infile  while 2 gt  gt logfile appends standard error to the end of the file named logfile   If you don t specify a number  then input redirection defaults to fd 0   lt  is the same as 0 lt    while output redirection defaults to fd 1   gt  is the same as 1 gt     Also  you can combine file descriptors together  2 gt  amp 1 means  send standard error wherever standard output is going   That means that you get a single stream of output that includes both standard out and standard error intermixed with no way to separate them anymore  but it also means that you can include standard error in a pipe    So the sequence  gt  dev null 2 gt  amp 1 means  send standard output to  dev null   which is a special device that just throws away whatever you write to it   and then send standard error to wherever standard output is going   which we just made sure was  dev null   Basically   throw away whatever this command writes to either file descriptor      When nohup detects that neither its standard error nor output is attached to a terminal  it doesn t bother to create nohup out  but assumes that the output is already redirected where the user wants it to go   The  dev null device works for input  too  if you run a command with  lt  dev null  then any attempt by that command to read from standard input will instantly encounter end-of-file  Note that the merge syntax won t have the same effect here  it only works to point a file descriptor to another one that s open in the same direction  input or output   The shell will let you do  gt  dev null  lt  amp 1  but that winds up creating a process with an input file descriptor open on an output stream  so instead of just hitting end-of-file  any read attempt will trigger a fatal  invalid file descriptor  error

User · Answer

Have you tried redirecting all three I O streams   nohup   yourprogram  gt  foo out 2 gt  foo err  lt   dev null  amp

User · Answer

You can run the below command   nohup  lt your command gt   amp   gt    lt outputfile gt  2 gt  amp 1  amp    e g  I have a nohup command inside script     Runjob sh  gt  sparkConcuurent out 2 gt  amp 1

User · Answer

sudo bash -c  nohup  opt viptel viptel bin log sh     amp  gt   dev null    amp    Redirecting the output of sudo causes sudo to reask for the password  thus an awkward mechanism is needed to do this variant

User · Answer

If you have a BASH shell on your mac linux in-front of you  you try out the below steps to understand the redirection practically    Create a 2 line script called zz sh     bin bash echo  Hello  This is a proper command  junk errorcommand    The echo command s output goes into STDOUT filestream  file descriptor 1   The error command s output goes into STDERR filestream  file descriptor 2    Currently  simply executing the script sends both STDOUT and STDERR to the screen     zz sh   Now start with the standard redirection    zz sh  gt  zfile txt   In the above   echo   STDOUT  goes into the zfile txt  Whereas  error   STDERR  is displayed on the screen   The above is the same as    zz sh 1 gt  zfile txt   Now you can try the opposite  and redirect  error  STDERR into the file  The STDOUT from  echo  command goes to the screen   zz sh 2 gt  zfile txt   Combining the above two  you get   zz sh 1 gt  zfile txt 2 gt  amp 1   Explanation    FIRST  send STDOUT 1 to zfile txt  THEN  send STDERR 2 to STDOUT 1 itself  by using  amp 1 pointer   Therefore  both 1 and 2 goes into the same file  zfile txt    Eventually  you can pack the whole thing inside  nohup command  amp  to run it in the background   nohup zz sh 1 gt  zfile txt 2 gt  amp 1 amp

User · Answer

You might want to use the detach program  You use it like nohup but it doesn t produce an output log unless you tell it to  Here is the man page   NAME        detach - run a command after detaching from the terminal  SYNOPSIS        detach  options   --  command  args          Forks  a  new process  detaches is from the terminal  and executes com-        mand with the specified arguments   OPTIONS        detach recognizes a couple of options  which are discussed below    The        special  option -- is used to signal that the rest of the arguments are        the command and args to be passed to it          -e file               Connect file to the standard error of the command          -f     Run in the foreground  do not fork           -i file               Connect file to the standard input of the command          -o file               Connect file to the standard output of the command          -p file               Write the pid of the detached process to file   EXAMPLE        detach xterm         Start an xterm that will not be closed when the current shell exits   AUTHOR        detach was written by Robbert Haarman   See  http   inglorion net   for        contact information    Note I have no affiliation with the author of the program  I m only a satisfied user of the program

[unix] How do I use the nohup command without getting nohup.out?

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