Standard IO Redirection

The control of IO (Input/Output) redirection can be managed using the keys StdIn, StdOut, and StdErr within the [Main] section.

If none of the StdIn, StdOut, and StdErr keys are defined, the default behavior is to use the s6-log program. In this case, you can use the [Logger] section to modify the behavior of s6-log (see the [Logger] section documentation) such as log file rotation.

It should be noted that administrative permissions may be required for values tty, console, and syslog. A service run as a regular user will not have the necessary rights to access, for example, tty3.

Depending on the definition and combination of these keys, the behavior will be as follows:

StdIn

This key allows redirection of the Standard Input (file descriptor 0) of the service. As indicated in the documentation for the [Main] section, this key accepts several values.

If the key is not defined, it will take the value of StdOut if StdOut is set to s6log or if StdOut is not defined at all.

Redefinition of StdOut and StdErr based on the value of StdIn

• StdIn = tty:/path/to/tty

  In this case, the value of StdOut will be the same as StdIn regardless of the value set for StdOut.

• StdIn = s6log

  In this case, the value of StdOut will be s6log and the value of StdErr will be inherit regardless of the values set for StdOut and StdErr.

• For the values null, parent, and close, the values of StdOut and StdErr will not be redefined.

StdOut

This key allows redirection of the Standard Output (file descriptor 1) of the service. As indicated in the documentation for the [Main] section, it accepts several values.

If the key is not defined, it will take the value of StdIn as follows:

• If StdIn is set to tty or s6log, the StdOut key will take the same value tty or s6log respectively.
• If StdIn is set to null, StdOut will take the value inherit.
• If StdIn is set to parent or close, StdOut will take the value parent.

In all other cases, StdOut will take the value s6log.

This key takes precedence over StdErr depending on the chosen value.

Redefinition of StdErr based on the value of StdOut

• If the value of StdOut is equal to StdErr, StdErr will be set to inherit(e.g. StdOut = tty:/dev/tty2 AND StdErr = tty:/dev/tty2).

• StdOut = syslog

  In this case, the value of StdErr will be the same as StdOut regardless of the value set for StdErr.

• For the values tty, file, console, s6log, inherit, null, parent, and close, StdErr will not be redefined.

StdErr

This key allows redirection of the Standard Error (file descriptor 2) of the service. As indicated in the documentation for the [Main] section, it accepts several values.

If the key is not defined, it will be set to inherit.

In all other cases, no redefinition is made.

Options defined on !log

If the Options key in the [Main] section defines !log, the [Logger] section will have no effect. Additionally, if the keys StdIn, StdOut, or StdErr are set to s6log or not defined at all, StdIn, StdOut, and StdErr will take the value of parent process.

Examples

Let's take some examples:

• A frontend file with

  [Main]
  Type = classic
  Description = "connman daemon"
  Version = 0.0.1
  User = ( root )
  
  [Start]
  Execute = ( connmand -n --nobacktrace --nodnsproxy )
  

  is strictly equal to

  [Main]
  Type = classic
  Description = "connman daemon"
  Version = 0.0.1
  User = ( root )
  StdIn = s6log
  StdOut = s6log
  StdErr = inherit
  
  [Start]
  Execute = ( connmand -n --nobacktrace --nodnsproxy )
  

• A frontend file with

  [Main]
  Type = classic
  Description = "connman daemon"
  Version = 0.0.1
  User = ( root )
  StdIn = s6log
  
  [Start]
  Execute = ( connmand -n --nobacktrace --nodnsproxy )
  

  is strictly equal to

  [Main]
  Type = classic
  Description = "connman daemon"
  Version = 0.0.1
  User = ( root )
  StdIn = s6log
  StdOut = s6log
  StdErr = inherit
  
  [Start]
  Execute = ( connmand -n --nobacktrace --nodnsproxy )
  

• A frontend file with

  [Main]
  Type = classic
  Description = "connman daemon"
  Version = 0.0.1
  User = ( root )
  StdOut = s6log
  
  [Start]
  Execute = ( connmand -n --nobacktrace --nodnsproxy )
  

  is strictly equal to

  [Main]
  Type = classic
  Description = "connman daemon"
  Version = 0.0.1
  User = ( root )
  StdIn = s6log
  StdOut = s6log
  StdErr = inherit
  
  [Start]
  Execute = ( connmand -n --nobacktrace --nodnsproxy )
  

• A frontend file with

  [Main]
  Type = classic
  Description = "connman daemon"
  Version = 0.0.1
  User = ( root )
  StdIn = tty:/dev/tty1
  
  [Start]
  Execute = ( connmand -n --nobacktrace --nodnsproxy )
  

  is strictly equal to

  [Main]
  Type = classic
  Description = "connman daemon"
  Version = 0.0.1
  User = ( root )
  StdIn = tty:/dev/tty1
  StdOut = tty:/dev/tty1
  StdErr = inherit
  
  [Start]
  Execute = ( connmand -n --nobacktrace --nodnsproxy )
  

• A frontend file with

  [Main]
  Type = classic
  Description = "connman daemon"
  Version = 0.0.1
  User = ( root )
  StdIn = tty:/dev/tty1
  StdOut = syslog
  
  [Start]
  Execute = ( connmand -n --nobacktrace --nodnsproxy )
  

  is strictly equal to

  [Main]
  Type = classic
  Description = "connman daemon"
  Version = 0.0.1
  User = ( root )
  StdIn = tty:/dev/tty1
  StdOut = tty:/dev/tty1
  StdErr = inherit
  
  [Start]
  Execute = ( connmand -n --nobacktrace --nodnsproxy )
  

• A frontend file with

  [Main]
  Type = classic
  Description = "connman daemon"
  Version = 0.0.1
  User = ( root )
  StdIn = null
  StdOut = syslog
  
  [Start]
  Execute = ( connmand -n --nobacktrace --nodnsproxy )
  

  is strictly equal to

  [Main]
  Type = classic
  Description = "connman daemon"
  Version = 0.0.1
  User = ( root )
  StdIn = null
  StdOut = syslog
  StdErr = syslog
  
  [Start]
  Execute = ( connmand -n --nobacktrace --nodnsproxy )
  

• A frontend file with

  [Main]
  Type = classic
  Description = "connman daemon"
  Version = 0.0.1
  User = ( root )
  StdIn = null
  
  [Start]
  Execute = ( connmand -n --nobacktrace --nodnsproxy )
  

  is strictly equal to

  [Main]
  Type = classic
  Description = "connman daemon"
  Version = 0.0.1
  User = ( root )
  StdIn = null
  StdOut = inherit
  StdErr = inherit
  
  [Start]
  Execute = ( connmand -n --nobacktrace --nodnsproxy )
  

• A frontend file with

  [Main]
  Type = classic
  Description = "connman daemon"
  Version = 0.0.1
  User = ( root )
  StdIn = close
  
  [Start]
  Execute = ( connmand -n --nobacktrace --nodnsproxy )
  

  is strictly equal to

  [Main]
  Type = classic
  Description = "connman daemon"
  Version = 0.0.1
  User = ( root )
  StdIn = close
  StdOut = parent
  StdErr = inherit
  
  [Start]
  Execute = ( connmand -n --nobacktrace --nodnsproxy )
  

• A frontend file with

  [Main]
  Type = classic
  Description = "connman daemon"
  Version = 0.0.1
  User = ( root )
  StdOut = syslog
  
  [Start]
  Execute = ( connmand -n --nobacktrace --nodnsproxy )
  

  is strictly equal to

  [Main]
  Type = classic
  Description = "connman daemon"
  Version = 0.0.1
  User = ( root )
  StdIn = parent
  StdOut = syslog
  StdErr = syslog
  
  [Start]
  Execute = ( connmand -n --nobacktrace --nodnsproxy )
  

• A frontend file with

  [Main]
  Type = classic
  Description = "connman daemon"
  Version = 0.0.1
  User = ( root )
  StdOut = tty:/dev/tty1
  
  [Start]
  Execute = ( connmand -n --nobacktrace --nodnsproxy )
  

  is strictly equal to

  [Main]
  Type = classic
  Description = "connman daemon"
  Version = 0.0.1
  User = ( root )
  StdIn = parent
  StdOut = tty:/dev/tty1
  StdErr = inherit
  
  [Start]
  Execute = ( connmand -n --nobacktrace --nodnsproxy )
  

• A frontend file with

  [Main]
  Type = classic
  Description = "connman daemon"
  Version = 0.0.1
  User = ( root )
  StdOut = tty:/dev/tty1
  StdErr = file:/var/log/connman.log
  
  [Start]
  Execute = ( connmand -n --nobacktrace --nodnsproxy )
  

  is strictly equal to

  [Main]
  Type = classic
  Description = "connman daemon"
  Version = 0.0.1
  User = ( root )
  StdIn = parent
  StdOut = tty:/dev/tty1
  StdErr = file:/var/log/connman.log
  
  [Start]
  Execute = ( connmand -n --nobacktrace --nodnsproxy )
  

• A frontend file with

  [Main]
  Type = classic
  Description = "connman daemon"
  Version = 0.0.1
  User = ( root )
  Options = (!log)
  
  [Start]
  Execute = ( connmand -n --nobacktrace --nodnsproxy )
  

  is strictly equal to

  [Main]
  Type = classic
  Description = "connman daemon"
  Version = 0.0.1
  User = ( root )
  Options = (!log)
  StdIn = parent
  StdOut = parent
  StdErr = parent
  
  [Start]
  Execute = ( connmand -n --nobacktrace --nodnsproxy )
  

• A frontend file with

  [Main]
  Type = classic
  Description = "connman daemon"
  Version = 0.0.1
  User = ( root )
  Options = (!log)
  StdOut = s6log
  StdErr = file:/var/log/connmand.log
  
  [Start]
  Execute = ( connmand -n --nobacktrace --nodnsproxy )
  

  is strictly equal to

  [Main]
  Type = classic
  Description = "connman daemon"
  Version = 0.0.1
  User = ( root )
  Options = (!log)
  StdIn = parent
  StdOut = parent
  StdErr = file:/var/log/connmand.log
  
  [Start]
  Execute = ( connmand -n --nobacktrace --nodnsproxy )