How to read ros log file?

edit

Recently, I write a .launch file. But when I roslaunch it, I get the info as is shown below.

roslaunch turtlebot3_navigation multiple_navigation.launch 
... logging to /home/ise-admin/.ros/log/e4e33fd6-a16d-11e8-841a-509a4c311940/roslaunch-ise-linux-1-5449.log
Checking log directory for disk usage. This may take awhile.
Press Ctrl-C to interrupt
Done checking log file disk usage. Usage is <1GB.

Invalid roslaunch XML syntax: not well-formed (invalid token): line 29, column 83
The traceback for the exception was written to the log file

In order to find out where are the errors, I hope to open the log file.

cd `roslaunch-logs`
ls
first_tb3-amcl-4-stdout.log         roslaunch-ise-linux-1-3015.log
map_server-2-stdout.log             roslaunch-ise-linux-1-32614.log
master.log                          roslaunch-ise-linux-1-32683.log
robot1-spawn_minibot_model-2.log    roslaunch-ise-linux-1-32749.log
robot1-spawn_minibot_model-3.log    roslaunch-ise-linux-1-3598.log
robot2-spawn_minibot_model-4.log    roslaunch-ise-linux-1-415.log
robot2-spawn_minibot_model-5.log    roslaunch-ise-linux-1-4348.log
robot_state_publisher-1-stdout.log  roslaunch-ise-linux-1-791.log
roslaunch-ise-linux-1-23504.log     rosout-1-stdout.log
roslaunch-ise-linux-1-23544.log     rosout.log
roslaunch-ise-linux-1-23565.log     rviz-9-stdout.log
roslaunch-ise-linux-1-23628.log     second_tb3-amcl-6-stdout.log
roslaunch-ise-linux-1-24416.log     tb3_0-spawn_urdf-4.log
roslaunch-ise-linux-1-24423.log     tb3_0-spawn_urdf-4-stdout.log
roslaunch-ise-linux-1-25479.log     tb3_1-spawn_urdf-6.log
roslaunch-ise-linux-1-25593.log     tb3_1-spawn_urdf-6-stdout.log
roslaunch-ise-linux-1-25811.log     tb3_2-spawn_urdf-8.log
roslaunch-ise-linux-1-26965.log     tb3_2-spawn_urdf-8-stdout.log
roslaunch-ise-linux-1-27793.log     third_tb3-amcl-8-stdout.log

It seems that the log file is temporary, right?