Update cheatsheets

tldr/linux/systemctl-whoami

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+---
+syntax: markdown
+tags: [tldr, linux]
+source: https://github.com/tldr-pages/tldr.git
+---
+# systemctl whoami
+
+> Show units that processes belong to.
+> If no PID is specified, shows the unit the `systemctl` command itself is invoked in.
+> More information: <https://www.freedesktop.org/software/systemd/man/latest/systemctl.html#whoami%20%5BPID%E2%80%A6%5D>.
+
+- Show the unit of the current shell (where `systemctl` is running):
+
+`systemctl whoami`
+
+- Show the unit of the current shell in user service manager (services managed for your login session):
+
+`systemctl --user whoami`
+
+- Show the unit a specific process belongs to:
+
+`systemctl whoami {{pid}}`
+
+- Show the units for multiple processes:
+
+`systemctl whoami {{pid1 pid2 ...}}`