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Dual-comb spectroscopy (DCS), without moving mirrors, enables fast optical sampling of molecular vibrations and results in high-resolution and high-accuracy Fourier-transform spectra. This motionless technique holds much promise in gas sensing and environmental monitoring. However, in many cases, these applications require a mature device continuously operating for days or even months, thus posing a challenge to long-term stability of this delicate technique. In this paper, we demonstrate the feasibility of DCS for long-term routine spectral monitoring. A compact dual-comb spectrometer is built based on adaptive sampling and simple frequency stabilization schemes. The spectrometer is ceaselessly recording and displaying, in real time, transmission spectra of a phase-shifted fiber Bragg grating and of gas-phase samples for over 1200 h (50 days). We spectroscopically validate the system by measuring absorption lines of ν1 + ν3 band of C₂H₂ and of 2ν ₃ band of CH₄ and comparing the experimental data with HITRAN database.