What does at the end of a linux command mean

Question

I am a system administrator and I have been asked to run a linux script to clean the system   The command is this   perl script pl  gt  output log  amp    so this command is ending with a  amp  sign  is there any special significance of it   I have basic knowledge of shell but I have never seen this before

User · Answer

I don   t know for sure but I   m reading a book right now and what I am getting is that a program need to handle its signal   as when I press CTRL-C   Now a program can use SIG IGN to ignore all signals or SIG DFL to restore the default action   Now if you do   command  amp  then this process running as background process simply ignores all signals that will occur  For foreground processes these signals are not ignored

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In addition  you can use the   amp   sign to run many processes through one  1  ssh connections in order to  to keep minimum number of terminals  For example  I have one process that listens for messages in order to extract files  the second process listens for messages in order to upload files  Using the   amp   I can run both services in one terminal  through single ssh connection to my server       I just realized that these processes running through the   amp   will also  stay alive  after ssh session is closed  pretty neat and useful if your connection to the server is interrupted

User · Answer

When not told otherwise commands take over the foreground  You only have one  foreground  process running in a single shell session  The  amp  symbol instructs commands to run in a background process and immediately returns to the command line for additional commands   sh my script sh  amp    A background process will not stay alive after the shell session is closed  SIGHUP terminates all running processes  By default anyway  If your command is long-running or runs indefinitely  ie  microservice  you need to pr-pend it with nohup so it remains running after you disconnect from the session   nohup sh my script sh  amp    EDIT  There does appear to be a gray area regarding the closing of background processes when  amp  is used  Just be aware that the shell may close your process depending on your OS and local configurations  particularly on CENTOS RHEL    https   serverfault com a 117157

User · Answer

The  amp  makes the command run in the background   From man bash      If a command is terminated by the control operator  amp   the shell   executes the command in the background in a subshell   The shell does   not wait for the command to finish   and          the  return status is 0

[linux] What does "&" at the end of a linux command mean?

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